Category: Troubleshooting & Maintenance

Before calling a certified mitigator for an inspection or service visit — which costs $150–$300 — there are several things a homeowner can check in 30 minutes that will either resolve the issue, inform the contractor call with specific findings, or confirm that professional service is genuinely needed. This checklist covers the complete self-inspection sequence for an ASD radon mitigation system, organized by location in the home.

What You Need

• A flashlight or phone light
• A stepladder for attic access (if the fan is in the attic)
• A smartphone to photograph anything unusual
• This checklist

No specialized tools are required for this inspection. Everything on this list is assessable by a homeowner with basic observational ability and safe access to the fan location.

Step 1: Check the Manometer (Living Space — 30 Seconds)

Find the U-tube manometer — the liquid-filled gauge mounted on the visible portion of the riser pipe, typically in the basement, utility room, or closet. Observe the liquid level:

• ✅ Liquid displaced (one side higher): Fan is generating negative pressure. System is operating. Continue checklist to confirm no other issues.
• ❌ Liquid level (equal on both sides): Fan is not generating suction. Proceed to Step 2 before calling a contractor — there may be a simple fix.

Step 2: If Manometer Shows No Pressure — Check Power

• Go to the fan location (attic, exterior, or garage). Is the fan running? Can you hear or feel airflow from the discharge?
• If the fan appears not to be running: check the outlet by plugging in a lamp or phone charger. Is the outlet live?
• Check the circuit breaker panel for the circuit supplying the fan outlet — is any breaker tripped?
• If power is confirmed at the outlet but the fan is not running: the fan has likely failed. This requires professional fan replacement — there is no user-serviceable fix for a burned-out fan motor.
• If the outlet has no power (breaker tripped): reset the breaker. If it trips again immediately, there is a wiring issue — do not continue resetting; contact an electrician.

Step 3: Fan Location Inspection

Access the fan location safely. Bring your flashlight.

• ✅ Fan housing: no visible cracks or damage
• ❌ Fan housing: cracks visible — fan must be replaced regardless of whether it still runs (cracked housing discharges radon at the fan location)
• ✅ Inlet pipe connection (from below): secure, no gaps, no sign of separation
• ❌ Inlet connection: loose or separated — this is an air leak that reduces fan efficiency; pipe must be reconnected and re-cemented
• ✅ Outlet pipe connection (to discharge): secure, no gaps
• ❌ Outlet connection: loose or separated — reconnect and re-cement
• ✅ Fan mounting: stable, not in contact with adjacent framing
• ❌ Fan touching adjacent framing: add rubber isolation pad or adjust mounting
• ✅ Electrical connection: undamaged power cord or secure hardwired connection
• ❌ Damaged power cord: do not operate — contact an electrician or the original installer

Step 4: Discharge Cap Inspection

• ✅ Cap is intact and undamaged
• ❌ Cap is cracked, missing, or severely corroded — replace the cap; this is a DIY-accessible fix ($15–$30 for a standard 3″ PVC weatherproof cap)
• ✅ Cap opening is unobstructed — no bird nesting, debris, or ice visible
• ❌ Cap is obstructed — clear the obstruction. For ice: this is a cold-climate common issue; wrapping the pipe in heat tape near the cap can prevent recurrence.
• ✅ Pipe below the cap is secure and has not shifted in wind or from thermal movement
• ❌ Pipe has shifted or become unsecured — restrain with appropriate pipe strap or bracket

Step 5: Visible Riser Pipe Inspection

• ✅ Pipe is physically intact — no visible cracks or impact damage
• ❌ Pipe is cracked or damaged — section must be replaced by a professional
• ✅ All visible joints show cemented connections (purple/gray ring visible at each joint)
• ❌ Joints appear dry-fitted (no cement ring visible) — these are air leaks that must be re-cemented; this is professional work if in a hard-to-access location
• ✅ Pipe is strapped to framing every 4–6 feet
• ❌ Loose or missing pipe straps — tighten or add straps; this is a DIY-accessible fix
• ✅ Required AARST warning label is present and legible
• ❌ Label is missing or unreadable — obtain a replacement label from a radon supply distributor or your original installer

Step 6: Suction Point and Slab Inspection

• ✅ Core hole seal around riser pipe at slab is intact — no gaps or crumbling
• ❌ Core hole seal is deteriorated or gapped — reseal with hydraulic cement (DIY-accessible)
• ✅ No new visible slab cracks since last inspection
• ❌ New slab cracks visible — photograph and document; seal wide cracks with polyurethane caulk; schedule a retest to confirm these new pathways are not affecting radon levels
• ✅ Expansion joints and control joints show intact sealant
• ❌ Sealant is cracked, pulled away, or missing in joints — reapply polyurethane caulk (DIY-accessible)
• ✅ Sump pit (if present) has an airtight lid that is secure
• ❌ Sump lid is loose, damaged, or missing — this is a significant radon bypass pathway; replace or repair the sump lid immediately

Interpreting Your Inspection Results

All ✅ — System Appears Intact

If all checkpoints pass and the manometer shows displaced fluid, the system is operating normally. If you are conducting this inspection because of elevated radon test results, a professional diagnostic visit is still advisable — some performance issues (fan approaching end of life, partial suction field coverage) are not apparent from visual inspection alone.

One or More ❌ — Action Required

For DIY-accessible fixes (pipe straps, sealant, sump lid, discharge cap): address these immediately. For items requiring professional work (cracked housing, separated pipe joints in inaccessible locations, failed fan, hardwired electrical issues): contact your original installer under the workmanship warranty if within the warranty period, or any certified mitigator for an out-of-warranty service call.

Frequently Asked Questions

How do I know if my radon mitigation system needs service?

Run through this inspection checklist: check the manometer (displaced fluid = running), inspect the fan housing and pipe connections, confirm the discharge cap is unobstructed, and examine the visible pipe and slab sealing. If all items pass and the manometer shows the system is running, conduct a 48-hour radon test to confirm actual performance. If the test shows elevated levels despite the system appearing operational, schedule a professional diagnostic visit.

Can I do this inspection myself or do I need a professional?

This entire inspection is accessible to any homeowner comfortable with attic access and basic observation. No specialized tools or training are required. Professional involvement is needed only when the inspection reveals issues that require construction work (re-cementing separated pipe joints in inaccessible locations, fan replacement, electrical repairs) or when the visual inspection passes but elevated radon levels require deeper diagnostic investigation.

What is the most important thing to check on my radon system?

The U-tube manometer — check it first, check it monthly. A displaced liquid column tells you in 5 seconds that the fan is running and generating negative pressure. Everything else on this checklist refines your understanding of system integrity and performance, but the manometer is the primary indicator that can reveal the most critical failure mode (fan stopped) without any tools or expertise.

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Related Radon Resources

• Radon Still High After Mitigation: Complete Diagnosis Guide
• Radon Fan Making Noise: Causes and Diagnosis
• Radon Fan Replacement: When, How, and What Fan to Buy
• 5-Year Radon System Maintenance Schedule

Owners of continuous radon monitors frequently see readings that spike dramatically — a home that averages 1.2 pCi/L shows 8.0 pCi/L for a single hour, or a mitigated home that has run at 0.4 pCi/L for years suddenly shows 3.5 pCi/L for two days during a cold snap. Understanding what causes these spikes — and which spikes represent real, sustained changes versus transient fluctuations — is essential for using continuous monitoring data correctly and avoiding both unnecessary alarm and false reassurance.

The Fundamental Variability of Radon

Before examining specific spike causes, establish the baseline: radon levels in any home fluctuate continuously. Published research consistently shows day-to-day variation of 30–50% in residential radon concentrations, driven by weather, HVAC operation, and occupant behavior. A home with a true annual average of 2.0 pCi/L might show readings anywhere from 0.8 to 4.0 pCi/L during different 24-hour periods — all representing normal variation around the same underlying radon entry rate. A single hour reading of 5.0 pCi/L in that home does not mean the annual average has changed.

Consumer continuous monitors (Airthings, RadonEye, Corentium) display running averages alongside recent readings precisely because the hourly and daily data is too variable to act on directly. The 30-day and long-term average is the meaningful metric for mitigation and health decisions; single hourly readings are data points in a noisy time series.

Cause 1: Barometric Pressure Drop

This is the most common cause of significant short-term radon spikes. When atmospheric pressure drops — as a storm system approaches, a cold front passes, or during extended low-pressure weather patterns — the pressure differential between the sub-slab soil and the home’s interior increases. The soil acts like a sponge being released: more radon is drawn inward through any available pathway.

Radon spikes associated with barometric pressure drops are typically 24–72 hours in duration, track closely with storm timing, and return to near-baseline when pressure normalizes. Spikes of 2–3× the home’s baseline during a significant pressure drop are documented in the literature and are not indicative of system failure or a structural change.

A mitigated home’s ASD system partially dampens barometric-driven spikes because the fan maintains a consistent pressure differential at the sub-slab regardless of outdoor pressure — but it cannot fully eliminate them. During extreme pressure drops, even well-functioning mitigation systems may show temporary elevation above typical post-mitigation levels.

Cause 2: Whole-House Fan or Attic Fan Operation

Whole-house fans evacuate large volumes of air from the home, creating substantial negative pressure. This negative pressure draws replacement air from anywhere it can enter — including through foundation cracks, floor-wall joints, and other radon entry pathways. Running a whole-house fan can cause radon concentrations to spike significantly during operation, then return to normal when the fan is off.

If your continuous monitor shows spikes that correlate with whole-house fan use, the spike is real — the fan is drawing in radon-laden soil gas. The solution is either to stop using the fan at night (when radon entry is typically highest and the fan most frequently used), or to accept the trade-off between cooling and radon exposure during fan-operating periods.

Cause 3: HVAC System Operation

Forced-air HVAC systems can create cyclical radon variation in some homes. When the system operates in heating or cooling mode, it creates pressure changes that affect radon entry rate. In some configurations — particularly when the air handler draws return air from basement space — HVAC operation creates a period of slightly elevated radon entry followed by dilution from the conditioned air volume. This can show as a regular, cyclical pattern in continuous monitor data rather than a spike.

Fireplaces and wood stoves create strong negative pressure when operating, which can pull soil gas into the building. Radon readings during fireplace operation may be noticeably elevated, then return to normal after the fire dies and the flue is dampered.

Cause 4: Monitor Placement Issues

Continuous monitor placement can produce readings that appear to spike but are actually artifacts of the device’s location:

• Too close to the suction point: A monitor placed near the radon system’s suction pipe may show artificially low readings when the system is working well, and spikes when the system pressure changes
• Near a floor drain or sump pit: A monitor within 2–3 feet of an open sump pit or floor drain will show elevated readings that don’t represent room-average radon concentration
• In a confined space or closet: Restricted air circulation produces radon accumulation in the test location that doesn’t represent normal breathing-zone air
• Near an exterior wall or window: Air infiltration and stack effect drafts can produce local radon concentration variations near these locations

If you see persistent spikes that don’t correlate with weather events or HVAC operation, review the monitor placement. Move it to the center of the room, at breathing-zone height (2–5 feet above floor), away from the listed problem locations. Wait 7–10 days after moving to allow the running average to reflect the new location.

When a Spike Indicates a Real Problem

Not all spikes are transient weather-related events. These patterns warrant investigation:

• 30-day average increasing trend over 3–6 months: If the long-term average has been climbing — from 0.5 to 1.0 to 1.8 over six months — in a mitigated home, the system may be losing performance. Check the manometer, inspect the fan, and schedule a diagnostic visit.
• Sustained elevation above 4.0 pCi/L for more than 3–4 days: Transient barometric spikes typically resolve within 72 hours. Sustained elevation that persists through multiple pressure cycles suggests a structural change — new cracks, a separated pipe joint, a sump pit that has lost its seal — rather than a weather event.
• Sudden step-change that doesn’t resolve: A reading that jumps from 0.4 pCi/L to 3.0 pCi/L and stays there suggests a specific event — a pipe joint that separated, a sump lid that was displaced, or new construction activity that created a pathway. Investigate the system physically.
• Spikes correlating with specific activities in the home: Elevated readings consistently correlating with using the bathroom above the basement (vibration opening a crack), opening a specific door (pressure event), or other repeatable activities may indicate a specific, addressable entry pathway.

Frequently Asked Questions

My radon monitor showed 12 pCi/L during a storm — should I be worried?

A single storm-period spike to 12 pCi/L is likely a barometric pressure event, particularly if your long-term average is below 4.0 pCi/L and the reading returned to normal within 1–3 days after the storm. Check your 30-day average — if it remains well below 4.0 pCi/L, the spike does not require action. If it corresponds with a sustained rise in the long-term average, investigate the mitigation system.

Why does my radon monitor show higher readings at night?

Several reasons: overnight temperature drops strengthen the stack effect, HVAC may cycle differently at night, and outdoor pressure patterns often change overnight. Homes that are closed up tightly at night with less ventilation accumulate radon at slightly higher rates than during daytime when people open doors and windows. Overnight elevations of 20–40% above daytime baseline are common and normal in many homes.

How do I know if a spike on my monitor means the mitigation system stopped working?

Check the U-tube manometer — if the liquid is still displaced, the fan is still generating suction. If the spike correlates with a storm or pressure event and resolves within 72 hours, the system is likely functioning. If the spike is sustained, the long-term average is rising, or the manometer shows level fluid, the system requires investigation. A current radon test (48-hour charcoal canister) provides a definitive measurement that is less susceptible to the noise inherent in continuous monitor hourly data.

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Related Radon Resources

• Radon Still High After Mitigation: Diagnosis Guide
• Radon System Self-Inspection Checklist
• 5-Year Radon System Maintenance Schedule
• Radon Fan Making Noise: Causes and Diagnosis

A radon mitigation system is designed for a specific home configuration at a specific point in time. When that configuration changes — through renovation, addition, HVAC upgrade, or foundation work — the pressure dynamics the system was designed for may shift. Some changes are minor and require only awareness; others can significantly affect system performance and warrant a full retest. Knowing which renovations trigger the need for radon reevaluation protects both the occupants’ health and the integrity of any existing mitigation system.

Why Renovations Affect Radon Levels

Radon entry into a building is governed by pressure differential — the difference between indoor air pressure and sub-slab soil gas pressure. Anything that changes the building’s internal pressure, its air exchange rate, or the pathways between the soil and the living space can affect radon levels. Renovations frequently do all three:

• Pressure changes: New HVAC equipment, additional exhaust fans, or air sealing that changes the building’s baseline pressure relative to the sub-slab affects how aggressively soil gas is drawn in
• New entry pathways: Any penetration through the foundation, slab, or below-grade walls — for plumbing, electrical conduit, HVAC ductwork — creates a new potential radon entry point
• Increased occupancy of lower levels: Finishing a basement increases the time occupants spend in the highest-radon zone, even without changing actual concentrations
• Disruption of existing sealing: Construction activity near the slab can damage the polyurethane sealant in expansion joints or cracks, reopening closed pathways

Basement Finishing: The Highest-Priority Renovation for Radon

Finishing an unfinished basement — converting it from a utility space to livable area with drywall, flooring, and potentially sleeping rooms — is the renovation most closely associated with radon health risk, for a straightforward reason: people will now spend significant time in the space with the highest radon concentration in the home.

Test Before Finishing

If you have not previously tested the basement for radon, test before finishing begins. Installing drywall and flooring over an untested basement is the construction equivalent of learning about a mold problem after you have encapsulated it. If the basement tests elevated, mitigation before finishing is dramatically less expensive and disruptive than post-finish mitigation — you avoid drilling through finished flooring, routing pipe through finished walls, and accessing spaces that are now concealed behind drywall.

Retest After Finishing

Even in a mitigated home, retest after basement finishing is complete and the space has been occupied for at least 30 days. Finishing work involves multiple trades — each may have created new penetrations through the slab or disrupted existing sealant. The new flooring, drywall, and HVAC configuration changes the room’s air circulation patterns and the relationship between the living space and the sub-slab zone. Confirming the mitigation system is still achieving target levels in the finished space validates that the system design remains adequate for the new configuration.

RRNC Opportunity During Finishing

If a home does not have a mitigation system and the basement is being finished for the first time, this is the ideal moment to install one — before the walls are closed and the flooring is down. The suction point can be placed without concern for finished flooring, pipe routing is accessible through open wall cavities, and the fan can be positioned in the attic before ceiling access is lost to a drop ceiling or drywall.

HVAC System Changes

Heating, ventilation, and air conditioning changes can significantly alter building pressure dynamics:

New Forced-Air Systems or Furnaces

A forced-air furnace or air handler creates negative pressure in the space around it — drawing air from the building to supply combustion air or return air. In a basement or utility room, this suction effect can work against the mitigation system’s sub-slab depressurization or draw more radon into the living space when the system is running. Retest after installation of a new forced-air system, particularly if the air handler is located in the basement or utility room adjacent to the foundation.

Whole-House Fans and Attic Fans

Whole-house fans (large ceiling fans that exhaust hot air through attic vents) create significant negative pressure in the home during operation — potentially drawing more soil gas through any available foundation pathways. If a whole-house fan is installed, retest for radon with the fan operating under typical conditions, not just during closed-house conditions with the fan off. The radon test result under normal operating conditions (including fan use) is the relevant health exposure measurement.

HRV and ERV Installation

Heat Recovery Ventilators and Energy Recovery Ventilators change the building’s air exchange rate, which can affect both indoor radon concentration (higher ventilation = more dilution) and building pressure (balanced HRV/ERV affects pressure less than exhaust-only systems). Retest after HRV/ERV installation — the effect can go either direction, and confirming the result is important.

Home Additions

Adding a room or wing to a home introduces new foundation area that the existing mitigation system may not cover:

• A basement addition creates new sub-slab area that requires its own suction coverage — the original system’s suction field may not extend into the new space
• A crawl space addition requires ASMD coverage of the new crawl space footprint
• A slab-on-grade addition attached to a mitigated basement may have an isolated sub-slab zone that requires its own suction point
• New foundation penetrations for the addition’s utilities create new potential entry pathways

Retest after any structural addition, with the test device placed in the new addition’s lowest level. If elevated, extend the mitigation system coverage to include the new zone.

Foundation and Waterproofing Work

Foundation work — crack injection, waterproofing, underpinning, or any excavation adjacent to the foundation — changes the sub-slab environment. Crack injection fills a pathway that radon was previously entering through; this is beneficial but may redirect radon to other pathways. Interior waterproofing systems sometimes include drainage channels and sump pits that alter the sub-slab connectivity that the mitigation system depends on.

Retest after any significant foundation or waterproofing work. If interior waterproofing installed a drainage channel system, ensure the sump pit associated with that system is integrated into the radon mitigation system (airtight lid and connection to the fan), or assess whether the drainage channel has altered sub-slab connectivity in ways that require mitigation redesign.

Air Sealing and Insulation Projects

Significant air sealing of the building envelope — spray foam insulation in attic and crawl space rim joists, dense-pack cellulose in walls, window and door air sealing — changes the building’s natural ventilation rate and can affect indoor radon concentration:

• Tighter buildings have lower air exchange rates, meaning radon that enters accumulates to higher concentrations before diluting
• Tighter buildings may have stronger stack effect (less outdoor air infiltration means the pressure differential between basement and attic is more pronounced)
• A well-functioning mitigation system in a previously leaky building may perform differently in a significantly air-sealed building

Retest after significant weatherization or energy efficiency projects that dramatically reduce air infiltration.

Frequently Asked Questions

Do I need to retest for radon after finishing my basement?

Yes — both before finishing (to identify elevated levels before concealing access) and after finishing (to confirm the mitigation system is still performing adequately in the new configuration). Finishing a basement changes how the space is used, how it is ventilated, and potentially how the sub-slab zone connects to the living area.

Can a new furnace affect my radon levels?

Yes, particularly if the air handler or furnace is located in the basement or utility room adjacent to the foundation. Forced-air systems create negative pressure that can work against the mitigation system’s sub-slab depressurization. Retest after installing any new major HVAC equipment in the lower level of the home.

Will adding an addition to my house affect my radon mitigation system?

Potentially, yes. A structural addition introduces new foundation area (basement, crawl space, or slab) that the existing system may not cover, plus new utility penetrations through the foundation that create new entry pathways. Retest after any structural addition, with the device placed in the addition’s lowest level. If elevated, extend system coverage to the new zone.

Does air sealing my home affect radon levels?

It can. Significant air sealing reduces the natural ventilation that previously diluted indoor radon. A tighter building accumulates radon at higher concentrations per unit of soil gas entry. If you undertake a major weatherization project (spray foam, dense-pack insulation, comprehensive air sealing), retest for radon in the 30–60 days following completion.

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Related Radon Resources

• 5-Year Radon System Maintenance Schedule
• Radon Still High After Mitigation: Diagnosis Guide
• How to Test for Radon in Your Home
• Post-Mitigation Radon Testing

A radon mitigation fan runs 24 hours a day, 365 days a year — it is one of the hardest-working mechanical components in any home. Eventually, every fan reaches end of service life. Replacing it is one of the simpler home maintenance tasks: the pipe network stays entirely in place, only the fan swaps out, and in most cases the job takes under an hour. Understanding when replacement is needed, which fan to buy, and what the replacement process involves removes the anxiety from a task that is fundamentally straightforward.

When to Replace a Radon Fan

Radon fans should be replaced when any of the following apply:

• Grinding or squealing sounds: These sounds indicate bearing failure. Bearings in radon fans are permanently sealed and cannot be serviced — once they begin to fail, the fan must be replaced. The grinding phase typically lasts weeks to months before the fan seizes; do not wait for complete failure.
• Fan has stopped running: If the manometer shows level (not displaced) fluid and the fan is confirmed to have power, the motor has burned out or the fan has seized. Replace immediately — the system is providing no radon protection.
• Fan is over 15 years old (attic-mounted) or over 10 years old (exterior-mounted): Even a fan that is still running quietly at this age is approaching end of statistical service life. Proactive replacement before failure avoids discovering a failed fan on a radon retest or, worse, during a real estate transaction.
• Post-mitigation radon retest shows elevated levels and the fan is confirmed running: A fan that runs but generates insufficient suction (declining bearing efficiency, partial failure) may produce manometer displacement while no longer achieving adequate sub-slab depressurization. When elevated levels are confirmed by a retest and other causes are ruled out, fan replacement is the next diagnostic step.
• Fan housing is cracked: A cracked fan housing discharges radon at the fan location — even in an attic, this is unacceptable. Replace immediately.

How to Choose a Replacement Fan

Replace with the Same Model or Better

The simplest approach: replace with the identical fan model that was originally installed. The pipe connections are already sized to match, the electrical connection is in place, and you have confirmed performance data from the original installation. If the original fan achieved satisfactory post-mitigation results, the same model will achieve the same results.

The original fan model is typically stamped on a label on the fan housing. Take a photograph of this label before removal — it contains the model number, serial number, and manufacture date.

Upgrading the Fan Model

If post-mitigation radon levels have been creeping upward over the past several retest cycles, replacement is an opportunity to upgrade to a higher-capacity model that may achieve better sub-slab coverage. The common upgrade path:

• RP145 → RP265: step up from 20W/40CFM to 55W/75CFM at 0.5″ WC for homes where the original low-capacity fan was borderline
• RP265 → GP301/GP501: step up from mid-range to high-static for homes with dense aggregate or large footprints where current results are marginal

Note: upgrading fan capacity increases electricity consumption and can over-depressurize the sub-slab in homes with good aggregate — pulling too much conditioned air from the building into the soil. If there is no documented reason to upgrade (consistent post-mitigation results have been good for years), same-model replacement is preferable.

Common Replacement Fan Models and Where to Buy

• RadonAway RP145: 20W, ~40CFM at 0.5″ WC. Available from radon supply distributors, Home Depot (in some markets), and online retailers. Retail price: $80–$100.
• RadonAway RP265: 55W, ~75CFM at 0.5″ WC. The most common replacement fan for standard residential systems. Retail price: $100–$140.
• RadonAway GP301: 85W, high-static. For dense aggregate or large footprints. Retail price: $140–$180.
• RadonAway GP501: 90W, highest-capacity residential. Retail price: $150–$200.

Purchase from radon supply distributors (search “radon fan distributor [your state]”) or directly from manufacturers. Home Depot and Lowes carry radon fans in high-radon market regions. Online purchase is straightforward — ship to home, install within a few days.

The Replacement Process

Safety First

Before beginning any work on the fan: turn off power to the fan at the outlet or circuit breaker. Confirm the fan has stopped by checking the manometer (it will show level fluid within a minute of the fan stopping) or by listening at the attic access. Never work on a running fan.

Photograph Before Disconnecting

Before disconnecting the old fan, photograph the pipe connections, electrical connection, and fan orientation. This provides a reference for reconnecting the new fan in the same configuration.

Disconnecting the Old Fan

• Disconnect the fan from the electrical outlet or disconnect the hardwired connection (note: a licensed electrician should handle hardwired disconnection if you are not comfortable with electrical work)
• Loosen the pipe connections at the fan inlet and outlet — most radon fans use slip-fit PVC connections that are held by compression or friction, not cemented; confirm by twisting gently. If cemented (some installations), cutting the pipe near the fan flanges will be necessary.
• Remove the fan from its mounting bracket or straps
• Note the orientation of inlet (downward, toward sub-slab) and outlet (upward, toward discharge)

Installing the New Fan

• Mount the new fan in the same position and orientation as the old fan — inlet toward the sub-slab riser, outlet toward the discharge pipe
• Connect the pipe to the fan flanges. The connection should be firm — use the compression method for slip-fit flanges, or PVC primer and cement if re-cutting is needed. Do not use duct tape or foam — these are not appropriate radon pipe connections.
• Reconnect electrical power
• Turn on the fan and immediately check the manometer — the liquid should begin displacing within 1–2 minutes of the fan starting

Post-Replacement Verification

• Confirm the manometer shows displaced fluid within 5 minutes of the new fan starting
• Listen for normal operation — low hum, no grinding or rattling that was not present before
• Update your radon system documentation file with the replacement date and new fan model/serial number
• Conduct a post-replacement radon test (48-hour charcoal canister, placed 24+ hours after fan activation) to confirm the new fan is achieving adequate radon reduction

DIY vs. Professional Fan Replacement

Fan replacement is one of the more DIY-accessible radon tasks because no concrete drilling or pipe routing is involved — the existing infrastructure stays in place. Whether to DIY or hire a professional depends on:

• Attic access: If the fan is accessible through a standard attic hatch, DIY is straightforward. If access requires difficult ladder work or the attic is unconditioned in extreme weather, professional replacement may be worth the cost.
• Electrical work: Plug-in outlet connections are DIY-accessible. Hardwired connections require a licensed electrician for safe disconnection and reconnection — in most states, homeowners cannot do their own hardwired electrical work.
• State legal context: In states where owner-occupant radon work is permitted, fan replacement falls within that exemption. In states with strict licensing requirements, verify whether fan replacement (as opposed to full system installation) is covered by the owner-occupant exemption.
• Cost comparison: Fan cost $100–$180 (RP265 range). Professional replacement labor: $100–$250. Total professional cost: $200–$430. DIY saves the labor portion.

Frequently Asked Questions

How much does it cost to replace a radon fan?

Fan cost: $80–$200 depending on model (RP145 to GP501). Professional installation labor: $100–$250. Total professional replacement: $180–$450. DIY replacement saves the labor portion — approximately $100–$250 — but requires comfort with attic access and basic mechanical work. The pipe network stays in place; only the fan swaps out.

Can I replace my radon fan with a different model?

Yes, as long as the replacement fan’s flange connections fit the existing pipe size (typically 3-inch for residential systems). Upgrading capacity (e.g., RP265 to GP501) is possible but may not be necessary if the existing results were satisfactory. Downgrading capacity (e.g., GP501 to RP145) is not recommended without a professional diagnostic confirming lower capacity is sufficient.

How long does a radon fan replacement take?

For a certified professional with all equipment on hand: 30–90 minutes. For a competent DIY homeowner who has reviewed the process in advance: 60–120 minutes. The actual mechanical work is straightforward — attic access and safe ladder positioning typically take more time than the fan swap itself.

Do I need to retest for radon after replacing the fan?

Yes. A post-replacement radon test (48-hour charcoal canister, placed at least 24 hours after the new fan is activated) confirms the new fan is achieving adequate sub-slab depressurization. Fan replacement is an opportunity to verify the system is performing well — not just that a new fan is installed and running.

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Related Radon Resources

• Radon Fan Making Noise: Causes and Diagnosis
• Radon Still High After Mitigation: Diagnosis Guide
• Radon Mitigation Cost: Complete Breakdown
• How to Find and Hire a Good Radon Contractor

A radon mitigation system is one of the most set-and-forget home improvements available — but “set and forget” for 10 years without a single check is how homeowners discover their fan stopped working three years ago and they never noticed because no one looked at the manometer. This guide provides a structured 5-year maintenance schedule with specific tasks at monthly, annual, biennial, and 5-year intervals, plus a documentation approach that keeps your system’s history organized for future reference and eventual resale.

Monthly Tasks (5 Minutes or Less)

Check the U-Tube Manometer

Look at the liquid-filled gauge mounted on the riser pipe. The colored liquid column should be displaced — one side higher than the other. This indicates the fan is generating negative pressure in the pipe and the system is operating.

• Displaced liquid: Normal operation. No action needed. Make a mental note that you checked.
• Level liquid (equal on both sides): System is not generating suction. Check whether the fan outlet is live (plug a lamp into the same outlet), check the circuit breaker, and listen for fan operation. If power is confirmed and the manometer still shows no pressure: the fan has likely failed. Contact a certified mitigator.
• Liquid significantly lower than at installation: Fluid may have evaporated over years. Contact your installer for guidance on replenishing the manometer fluid.

Listen for the Fan

From a location below the attic-mounted fan — typically the room directly below — listen for the characteristic low hum of fan operation. New sounds (grinding, squealing, rattling) that were not present previously warrant investigation. Complete silence from a location where you previously could hear light fan operation suggests the fan may have stopped.

Annual Tasks (30–60 Minutes)

Physical Fan Inspection

Access the fan location (attic, exterior, or garage) and physically inspect:

• Fan housing: check for visible cracks in the plastic housing. Any crack warrants replacement regardless of whether the fan is still running — a cracked housing discharges radon at the fan location.
• Pipe connections at the fan inlet and outlet: confirm both connections are secure. Press gently on each connection — there should be zero movement.
• Fan wiring: confirm the power cord or hardwired connection is undamaged and not stressed or kinked.
• Mounting: confirm the fan is securely mounted and not vibrating against adjacent framing.

Discharge Cap Inspection

Inspect the discharge cap at the pipe termination (above the roof or gable end):

• Confirm the cap is intact — not cracked, missing, or corroded
• Confirm the cap opening is unobstructed — no bird nesting, leaf accumulation, or ice blocking
• Confirm the pipe below the cap is securely fastened and has not shifted
• For roof penetrations: inspect the pipe boot flashing for signs of water intrusion around the pipe

Visible Pipe and Label Inspection

• Inspect the visible riser pipe for cracks, impact damage, or separation at joints
• Confirm pipe straps are secure along the full visible run
• Confirm the required AARST warning label is still present and legible
• Note any new cracks in the slab near the suction point penetration — document with a photograph if new cracking is observed

Slab Sealing Condition

• Inspect the core hole seal at the slab — the hydraulic cement around the riser pipe should be intact with no gaps
• Inspect control joints and expansion joints for sealant degradation — polyurethane caulk has a useful life of 10–15 years; sealant that is cracked or pulling away should be reapplied
• Note any new visible slab cracks — photograph and date for your records

Every Two Years: Radon Retest

EPA recommends retesting a mitigated home every 2 years. The biennial radon test is the most important scheduled maintenance task because it is the only confirmation that the system is achieving adequate radon reduction, not just that it is running.

• Purchase a 48-hour charcoal canister test from a certified lab ($15–$30) or an alpha track long-term detector for a 90-day test ($25–$45)
• Place in the lowest livable level of the home, breathing zone height (20+ inches above floor), away from windows, HVAC vents, and the suction point
• Follow closed-house protocol for charcoal canisters
• Record the result and date in your radon system documentation file
• If the result is at or above 4.0 pCi/L: investigate immediately — see the diagnostic guide in the Troubleshooting section of this knowledge base
• If the result is between 2.0 and 4.0 pCi/L and was previously below 1.0 pCi/L: this trend warrants investigation even though it is below the action level — fan performance may be declining

Every 5 Years: Comprehensive System Review

Fan Performance Assessment

At the 5-year mark, consider having a certified mitigator conduct a professional diagnostic to measure actual fan performance — static pressure at the suction point, airflow rate, and suction field coverage. This provides a performance benchmark and allows comparison with original installation measurements if available. A fan that originally generated 0.10 inches of water column at the suction point and now generates 0.05 may be declining — useful to know before it fails.

At the 5-year mark, the RadonAway manufacturer warranty expires. If the fan has been experiencing any noise issues (grinding, squealing, increased vibration), 5 years is a good time to replace it proactively rather than waiting for failure — especially if it is an exterior-mounted fan with higher weather exposure.

Full Slab and Seal Inspection

After 5 years of foundation settling and seasonal thermal cycles, caulk and sealant that appeared intact at year one may have begun to fail. The 5-year mark is a good time for a thorough inspection of:

• All control joints and expansion joints — reapply polyurethane sealant where the existing sealant is cracked, pulled away, or missing
• The floor-wall joint perimeter — recaulk any sections showing gaps
• Plumbing penetrations — inspect hydraulic cement seals around any pipes through the slab
• Any cracks that have developed since original installation — seal with appropriate caulk or epoxy injection depending on width and activity

Documentation Update

At the 5-year mark, update your radon system documentation file with:

• All biennial retest results to date
• Any service performed — sealing work, fan replacement, suction point additions
• Current system performance assessment results if a professional diagnostic was conducted
• Updated photographs of the fan, manometer, visible pipe, and suction point area

Quick Reference: Maintenance Summary Table

Frequency	Task	Time Required
Monthly	Check U-tube manometer (displaced = good)	5 seconds
Monthly	Listen for unusual fan sounds	30 seconds
Annual	Physical fan inspection (housing, connections, mounting)	10–15 min
Annual	Discharge cap inspection	5 min
Annual	Visible pipe, straps, and label check	5 min
Annual	Slab sealing condition review	10–15 min
Every 2 years	48-hour radon retest (charcoal canister)	2 days + $15–$30
Every 5 years	Professional performance diagnostic (optional but recommended)	1–2 hrs + $150–$300
Every 5 years	Full slab and seal reapplication review	1–2 hrs
Year 7–10 (exterior fan) or Year 10–15 (attic fan)	Fan replacement (proactive or on failure)	1–2 hrs + $180–$450

Frequently Asked Questions

How often should I check my radon mitigation system?

Check the U-tube manometer monthly — 5 seconds, no tools required. Conduct an annual physical inspection of the fan, discharge cap, visible pipe, and slab sealing condition (30–60 minutes). Retest for radon every 2 years. At 5 years, consider a professional diagnostic of fan performance and a comprehensive slab seal inspection.

What maintenance does a radon fan require?

Radon fans require no internal servicing — they use permanently sealed, non-serviceable bearings. Maintenance consists of: monthly confirmation the fan is operating (via manometer), annual inspection for housing cracks and pipe connection security, and replacement when bearings begin to fail (indicated by grinding or squealing sounds) or when fan lifespan is reached (7–15 years depending on installation type).

How do I document my radon system for resale?

Maintain a home radon file containing: original pre-mitigation test result, installer documentation (name, certification number, installation date, system specs, fan model), original post-mitigation test result, all subsequent biennial retest results with dates, any service records, and fan warranty documentation. This file is what satisfies radon disclosure requirements and demonstrates to buyers that the system has been properly maintained and verified over time.

A radon mitigation fan should produce a low, steady hum that most homeowners never notice. When the fan starts making unfamiliar sounds — rattling, grinding, squealing, thumping, or loud vibration — something has changed. Some noise issues are minor and fixable with a simple adjustment; others are early warning signs of fan failure that require replacement before the fan stops working and radon levels rise. This guide covers the specific sounds, what they mean, and what to do about them.

Normal Radon Fan Operation: What You Should Hear

A properly installed, functioning radon fan in good condition produces:

• A low, continuous hum or white noise — similar to a bathroom exhaust fan, but usually quieter
• Airflow sound at the discharge cap termination (a soft rushing sound when you stand near it)
• Minor vibration transmitted through the pipe — the pipe may vibrate slightly, which is normal if the fan is running at normal speed

If this is the only sound your fan makes, it is operating normally. The following sections describe sounds that are not normal.

Vibration and Rattling

Sound Description

A rattling sound — metallic or plastic — that corresponds with fan operation and may intensify or diminish with vibration level. Sometimes described as a “buzzing” or “shaking” sound coming from the wall or attic.

Most Common Causes

• Loose pipe straps: The riser pipe is not adequately secured to framing members and is vibrating against the wall or adjacent surfaces. The pipe transmits fan vibration throughout its length, and a loose strap allows this vibration to become an audible rattle.
• Fan housing vibration: The fan itself is vibrating excessively — often because the impeller is slightly out of balance due to dust accumulation, minor damage, or manufacturing variation that becomes more pronounced as bearings age.
• Loose discharge cap: The cap at the pipe termination above the roof is loose and vibrating in wind — not a fan issue but produces a rattling sound that can be confused with fan noise.
• Fan touching adjacent structure: The fan housing or attached pipe is in contact with a joist, rafter, or attic floor material and transmitting vibration as noise.

Diagnosis and Fix

• Inspect pipe straps along the entire visible pipe run and tighten any that are loose; add additional straps if sections are unsecured
• Add foam pipe insulation wrap around the riser pipe where it passes through living space — this provides vibration damping and reduces transmitted noise
• Check the fan mounting — confirm it is secure and not in contact with adjacent framing
• Install vibration isolation feet or rubber mounting pads under the fan if available for your model (RadonAway makes isolation kits for some models)
• Inspect the discharge cap from outside and tighten any loose fasteners

Grinding or Squealing

Sound Description

A metallic grinding or high-pitched squealing sound that is new and distinct from the normal hum. May be intermittent or constant. Sometimes described as a “bearing noise.”

What This Means

Grinding and squealing almost always indicate bearing wear or bearing failure in the fan motor. Radon fans use permanently lubricated bearings that are not field-serviceable — when bearings begin to fail, the noise is a warning that the fan will stop working within weeks to months. This is not a fixable noise; it is a replacement indicator.

Action

Schedule fan replacement. If the fan is within its 5-year manufacturer warranty period, contact RadonAway or your fan manufacturer — warranty replacement is typically covered for defective bearings. If past warranty, contact a certified mitigator for fan replacement. Do not wait until the fan completely fails — a failed fan means no radon protection, and you may not notice it has stopped because the manometer can sometimes stay displaced briefly from residual pressure.

Thumping or Irregular Pulsing

Sound Description

A rhythmic thumping, bumping, or pulsing sound that corresponds to the fan’s rotation speed. Not the steady hum of normal operation but an irregular beat pattern.

Most Common Causes

• Debris in the fan impeller: A small piece of insulation, a leaf fragment, or other debris has entered the fan housing and is contacting the impeller blades with each rotation. This produces a thumping sound that may change in character as the debris shifts or is ejected.
• Damaged impeller: One or more impeller blades have been damaged (from debris or aging), creating an imbalance that produces a rhythmic thumping as the impeller rotates.
• Water in the pipe: Condensation accumulation in the pipe creates a thumping or gurgling sound as the fan’s airflow moves water that has pooled. This is more common in cold climates where the temperature differential causes condensation in the pipe run.

Diagnosis and Fix

• For debris: power the fan off (turn off at the outlet), allow the impeller to stop, and inspect inside the fan inlet for visible debris. Remove any debris. Restart the fan and confirm the noise is resolved. Never reach into a running fan.
• For impeller damage: fan replacement is typically required — a damaged impeller cannot be field-repaired and creates ongoing vibration that accelerates bearing wear.
• For water: ensure the pipe has adequate slope back toward the suction point (condensate should drain back to the sub-slab, not pool in the pipe). In extreme cold-climate cases, adding pipe insulation to the attic section of the riser reduces condensation.

Sudden Loud Operation (New Loud Noise)

If a fan that previously operated quietly has suddenly become much louder without changing its fundamental hum character, check:

• Discharge cap obstruction: A bird nest, ice formation, or debris at the discharge cap creates back pressure that forces the fan to work harder and louder. Inspect the termination point and clear any obstruction.
• Pipe disconnection below the fan: If a pipe connection has separated below the fan, the fan is now pulling air from inside the attic or wall cavity instead of from the sub-slab. This produces louder operation (less resistance) and means the system is no longer mitigating radon.
• Loss of sub-slab connectivity: A significant change in sub-slab conditions (water infiltration filling aggregate, major settling) can change the fan’s load, altering operating sound.

Complete Silence (Fan Has Stopped)

If you can no longer hear the fan at all from its previous location:

• Check the outlet — test with another device to confirm power is present
• Check the circuit breaker for the outlet or circuit supplying the fan
• If power is confirmed and the fan is silent, the fan motor has failed — replacement is needed immediately. Check the manometer: if the liquid is level (not displaced), the system has stopped providing radon protection.

When to Replace vs. Repair

The practical decision guide:

• Replace immediately: Grinding/squealing sounds (bearing failure imminent), complete silence with confirmed power, visible cracks in fan housing, fan over 12 years old with any new noise
• Diagnose and possibly fix: Rattling/vibration (may be pipe strap issue, not fan), thumping (may be debris, not damage), sudden loudness (may be discharge obstruction)
• Monitor: Minor vibration increase in a fan under 8 years old with no other symptoms — continue monthly manometer checks and schedule a diagnostic visit

Frequently Asked Questions

Is it normal for a radon fan to make noise?

A low, steady hum is normal — comparable to a bathroom exhaust fan but usually quieter. Grinding, squealing, rattling, or thumping sounds are not normal and warrant investigation. Grinding and squealing in particular indicate bearing wear and approaching fan failure; the fan should be replaced before it stops working entirely.

How do I reduce radon fan noise?

For vibration and rattling: tighten or add pipe straps along the riser; add foam pipe insulation around the riser where it passes through living space; install rubber vibration isolation mounts under the fan. For legitimate bearing noise (grinding/squealing): fan replacement is the only solution. For a quiet existing fan that has become louder: inspect the discharge cap for obstruction and check all pipe connections for separation.

My radon fan is loud in the winter but quiet in summer — why?

Cold weather creates stronger stack effect, which increases the pressure differential the fan works against — it may operate more audibly when the building is more tightly sealed and pressure differentials are higher. Cold weather can also cause thermal contraction of PVC pipe that changes vibration transmission characteristics. If the seasonal variation is minor, this is not necessarily a problem. If it has become dramatically louder in winter, inspect the discharge cap for ice obstruction.

How long do radon fans last?

RadonAway fans carry a 5-year manufacturer warranty. Expected operational lifespan: 10–15 years for fans mounted in conditioned or semi-conditioned attic space; 7–12 years for fans mounted on exterior walls exposed to weather and temperature extremes. Grinding or squealing sounds typically appear 1–3 years before complete failure — treat them as the signal to schedule replacement rather than waiting for the fan to stop.

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Related Radon Resources

• Radon Still High After Mitigation: Diagnosis Guide
• Radon Fan Replacement: When, How, and What Fan to Buy
• Radon System Self-Inspection Checklist
• 5-Year Radon System Maintenance Schedule

A post-mitigation radon test that comes back above 4.0 pCi/L — or even above 2.0 pCi/L when you expected 0.5 — is a frustrating result, but it is not uncommon. National data suggests 10–15% of initial residential radon mitigation installations do not achieve target radon levels on the first attempt and require a callback or additional work. Understanding why post-mitigation results disappoint — and which specific cause applies to your situation — is the foundation for an efficient fix. This guide covers the ten most common causes, in roughly the order of how often they occur.

Before Diagnosing: Confirm the Test Was Valid

Before assuming the system failed, confirm the post-mitigation test was conducted correctly. A surprising number of elevated post-mitigation results are caused by testing error rather than system failure.

• Was the test placed at least 24 hours after the fan was activated? Testing before the system reaches equilibrium — especially in the first few hours — produces results that reflect the transition between un-mitigated and mitigated conditions, not steady-state performance.
• Were closed-house conditions maintained? Open windows or whole-house fans during the test produce artificially low results — and ironically, a test run while a contractor is completing the installation (doors opening and closing repeatedly) may show different conditions than steady-state. If closed-house conditions were compromised, retest.
• Was the device placed correctly? Test devices placed directly below the suction point, adjacent to the sump pit, or near an HVAC vent can produce atypical results. Retest with the device in the center of the lowest livable room, at breathing-zone height.
• Was the result from a professional continuous monitor? If so, review the hourly data log — spikes during the test period may indicate a specific event (windows opened, HVAC change) rather than system failure.

If the test was valid, proceed to diagnosing the system.

Cause 1: Insufficient Suction Field Coverage

How common: Very common — the most frequent cause of inadequate post-mitigation results.

What it is: The sub-slab vacuum created by the single suction point does not extend far enough to depressurize the entire slab footprint. Radon continues to enter through portions of the slab that are outside the effective suction radius.

How to diagnose: A mitigator can perform a post-installation suction field test: with the fan running, check for negative pressure at various points across the slab — at floor drains, near walls, at the far end of the basement from the suction point. If some areas show no negative pressure, the suction field is not covering the full footprint.

Fix: Add one or more additional suction points in the uncovered areas, piped back to the same fan via manifold. Cost: $150–$400 per additional point plus any necessary pipe work.

Cause 2: Unsealed Bypass Entry Pathways

How common: Very common — often overlooked during initial installation or appearing after.

What it is: Radon is entering the home through pathways that bypass the sub-slab vacuum entirely — directly through cracks, gaps, or penetrations in the slab, walls, or floor-wall joint that are not covered by the vacuum zone. A suction system creates negative pressure in the soil below the slab, but if radon can enter above the slab through an open pathway, the vacuum doesn’t help.

How to diagnose: Inspect the slab surface carefully for visible cracks, especially wider cracks at expansion joints, control joints, or around floor drains. Check the floor-wall joint perimeter — a small gap around the entire perimeter is a common high-volume entry pathway. Check around plumbing penetrations. A smoke pencil or incense stick held near suspected entry points while the fan runs can reveal inward air draw at unmitigated pathways — if smoke is pulled toward the floor, that pathway is admitting outside air (and radon) to the interior above the vacuum zone.

Fix: Seal all identified pathways. Expansion joints and control joints: polyurethane backer rod and caulk. Visible cracks: low-viscosity polyurethane caulk or epoxy injection. Floor-wall joint: polyurethane caulk run continuously around the perimeter. Plumbing penetrations: hydraulic cement. Cost: $50–$300 in materials for typical sealing work; more if a contractor is hired to do this systematically.

Cause 3: Fan Undersized for Sub-Slab Conditions

How common: Moderately common — particularly in homes where the pre-installation diagnostic was abbreviated or skipped.

What it is: The installed fan does not generate sufficient airflow or static pressure to adequately depressurize the sub-slab zone. This is more likely in homes with dense sub-slab fill (clay, sand, or compacted earth rather than gravel aggregate) that resist airflow, or in large-footprint homes where one suction point must cover a very large area.

How to diagnose: A mitigator can measure the static pressure at the suction point with the current fan running. If pressure is below the expected range for the aggregate conditions, the fan is undersized. Alternatively, if the fan is an RP145 or RP265 and the home has visibly poor aggregate conditions, upgrading to a higher-capacity fan is a reasonable diagnostic first step.

Fix: Upgrade the fan to a higher-capacity model. The pipe network stays in place; only the fan changes. Cost: $180–$450 for a new fan and installation labor. This is covered under most workmanship warranties when the original post-mitigation result exceeds the target level.

Cause 4: Block Wall Radon Entry (CMU Foundation)

How common: Common in homes with concrete masonry unit (CMU) block foundation walls — prevalent in pre-1975 construction in many regions.

What it is: CMU block foundation walls have hollow cores that communicate with the soil. Radon migrating through these cores enters the basement air directly from the wall, not from below the slab — so sub-slab depressurization alone does not address this pathway.

How to diagnose: Hold a smoke pencil near the interior face of the block wall while the ASD system is running. If smoke is pulled toward the wall (rather than downward toward the floor), the wall is a primary radon entry source that the floor-based suction is not addressing.

Fix: Block-wall depressurization — drill 2″–3″ holes through the interior face of the block wall just above the slab, and manifold them into the existing fan system or a dedicated second fan. Alternatively, applying a dense masonry sealer to the interior block wall face reduces the inward airflow from the hollow cores. Cost: $300–$600 for block-wall depressurization add-on.

Cause 5: Sump Pit Contributing Uncontrolled Entry

How common: Moderately common in homes with sump pits that are not integrated into the mitigation system.

What it is: An open or loosely covered sump pit is connected to the drain tile system that runs around the foundation perimeter — creating a direct, low-resistance pathway for radon from the soil into the basement air. Even if the slab is under negative pressure, a sump pit that is open to the basement atmosphere allows radon from the drain tile to enter freely above the vacuum zone.

Fix: Install an airtight sump pit lid with a pipe fitting connecting the pit to the ASD system. The sump pump continues to operate normally; the pit is now part of the vacuum network rather than a radon bypass. Cost: $100–$250 for the lid and connection work.

Cause 6: Floor Drains as Bypass Pathways

How common: Less common than sump pits but significant when present.

What it is: Floor drains that connect directly to the drain tile system or to perforated drainage pipes in the sub-slab can allow radon to enter the home through the open drain grate. The sub-slab vacuum may not extend into this pathway effectively.

Fix: Install a floor drain radon trap — a water-filled standpipe or a specialized radon-blocking floor drain insert that maintains a water seal preventing gas flow up the drain while still allowing water drainage. Cost: $30–$100 in materials, or a plumber for more complex situations.

Cause 7: Air Leaks in the Pipe System

How common: Uncommon with properly cemented PVC; more common in DIY installations or rushed professional work.

What it is: An air leak in the pipe system — at a dry-fitted joint, a cracked fitting, or where the pipe penetrates the slab — allows air to enter the system between the fan and the suction point. This reduces the negative pressure the fan generates at the sub-slab, degrading system performance.

How to diagnose: With the system running, hold a smoke pencil or incense stick near every pipe joint. Any inward smoke draw indicates an air leak at that location.

Fix: Seal the leak — PVC cement on dry-fitted joints, replacement of cracked fittings, or caulk/sealant at the pipe-slab interface. Cost: minimal in materials; professional labor adds $100–$250 if a contractor is needed.

Cause 8: Multiple Foundation Zones Not All Addressed

How common: Common in homes with additions, combination basement/crawl space, or split-level foundations.

What it is: The home has more than one foundation zone — perhaps a basement under the main house and a slab under an addition — and only one zone was mitigated. Radon from the unmitigated zone continues to enter the home.

Fix: Add mitigation coverage to the unaddressed foundation zone. This may require additional suction points manifolded to the existing system, or a separate system for an isolated zone. Cost: $600–$2,000 depending on the extent of unaddressed foundation.

Cause 9: Building Pressure Changes Since Installation

How common: This cause explains elevated re-test results more often than elevated initial post-mitigation results.

What it is: Changes to the building’s HVAC system, ventilation, or insulation since the mitigation system was designed have altered building pressure dynamics. A new whole-house fan, a high-efficiency furnace that creates more depressurization, or significant air sealing of the building envelope can change how the mitigation system performs relative to its original design.

Fix: A mitigator assesses the current building pressure conditions and re-optimizes the system — typically by adjusting fan capacity or adding suction points. Sometimes simply sealing combustion appliance infiltration points resolves the issue.

Cause 10: Elevated Seasonal or Weather Conditions During Testing

How common: Most relevant as an explanation for one elevated result in a series of previously low results.

What it is: A post-mitigation test conducted during a period of unusually low barometric pressure, strong winds, or other weather conditions that push the home’s natural radon level to a temporary peak. Even a well-functioning mitigation system cannot reduce the impact of a major barometric pressure drop to zero — it reduces it dramatically, but a 48-hour test during a significant weather event may show somewhat higher levels than the true long-term average.

Fix: Retest under more neutral weather conditions. If the second test also shows elevated results, weather is not the explanation and system diagnosis is needed.

Frequently Asked Questions

What should I do if my radon is still high after mitigation?

First, confirm the post-mitigation test was conducted correctly — proper placement, closed-house conditions, at least 24 hours after fan activation. If the test was valid and results are at or above 4.0 pCi/L, contact your installing contractor immediately. This is a workmanship warranty situation if the system is within the warranty period. The contractor should conduct a diagnostic visit to identify the specific cause and correct it at no charge under the warranty.

How long should I wait after mitigation before testing?

Place the post-mitigation test device at least 24 hours after the fan is activated, and run the test for a minimum of 48 hours under closed-house conditions. Testing in the first few hours of system operation captures the transition period, not steady-state performance. Most certified contractors include post-mitigation testing as part of their service — confirm whether this is in your contract.

Is it covered under warranty if radon is still high after mitigation?

Most certified radon mitigators provide a workmanship warranty covering callbacks when post-mitigation testing results exceed the target level (typically 4.0 pCi/L). Warranty duration ranges from 1 to 5 years depending on the contractor. The warranty should be specified in your original contract — review it before contacting the contractor so you understand what is and is not covered.

Can I fix an underperforming radon system myself?

Some fixes are DIY-accessible in states that permit owner-occupant radon work — particularly adding sealant to visible cracks, installing a sump pit lid, or cleaning a blocked floor drain. Others — adding suction points, upgrading the fan, adding block-wall depressurization — involve more significant construction work and are better suited to the installing contractor under warranty, or to a new certified mitigator if the original contractor is unresponsive or warranty has expired.

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Related Radon Resources

• How to Find and Hire a Good Radon Contractor
• Radon Fan Replacement: When, How, and What Fan to Buy
• Radon Fan Making Noise: Causes and Diagnosis
• Radon Mitigation System Maintenance Guide