Where to Place a Radon Test in Your Home

Radon test placement is not optional or approximate — it is the single most controllable variable in the measurement process. A correctly purchased device from a certified lab, placed in the wrong location, produces a misleading result. EPA’s placement protocol exists to ensure the result reflects actual exposure in the breathing zone of living areas, not the conditions in a corner of a mechanical room or under an HVAC vent.

Which Floor to Test

Always test in the lowest level of the home that is used or could be used as living space. This includes:

• Finished basements: Test here, even if the basement is used only occasionally
• Unfinished basements: Test here if the basement could be converted to living space in the future, or if family members spend any time there (laundry, exercise, storage retrieval)
• First floor (no basement): If there is no basement or crawl space, the first floor is the lowest testable level
• Slab-on-grade main level: Test on the main living floor if the home has no basement

Do not test only on the second or third floor if a basement exists. Radon accumulates most at the lowest points of the home — testing only upper floors systematically underestimates actual exposure in the most radon-concentrated zones.

Height: Breathing Zone Placement

Place the test device in the breathing zone:

• Minimum height: 20 inches (approximately 50 cm) above the floor
• Maximum height: No strict upper limit, but ceiling height (where air stratification may occur) is not appropriate
• Ideal range: Tabletop height (28–36 inches) to mid-wall (48–60 inches) — where occupants breathe while sitting or standing in the room

Placing a device directly on the floor is wrong — floor-level air is not breathing-zone air, and radon concentrations near the floor (especially on a concrete slab) may be artificially elevated due to proximity to the entry surface. Placing a device on a high shelf near the ceiling introduces stratification effects and may not represent the breathing zone.

Distance from Walls and Other Surfaces

• Minimum wall distance: 12 inches (30 cm) from any wall or vertical surface
• Window and door distance: Away from any window, door, or other exterior opening that creates air movement
• HVAC vent distance: At least 36 inches from any supply or return vent — HVAC airflow creates local turbulence that can either dilute or concentrate radon at the measurement point artificially
• Sump pit distance: Not near the sump pit — sump pits are radon point sources; proximity will produce artificially high readings that do not represent room-average concentration

Rooms to Avoid

EPA’s placement protocol explicitly excludes certain room types:

• Kitchens: Cooking exhaust fans create pressure differentials; moisture and humidity affect charcoal adsorption
• Bathrooms: Exhaust fans and high humidity; not representative of general living space
• Laundry rooms: Dryer exhaust creates pressure changes; humidity from washing
• Closets: Restricted airflow — not representative of breathing-zone air in the room
• Crawl spaces: Not a living area; radon in the crawl space does not directly represent living-space concentration
• Unheated garages: Not conditioned living space; pressure dynamics differ from the home interior

Ideal Room Characteristics

The ideal test location is:

• A room regularly used by occupants — bedroom, living room, family room, home office
• On the lowest floor with living activity
• Central to the room — not tucked against the radon-entry-pathway slab edge or a foundation wall
• Away from windows and exterior doors
• Not directly above or adjacent to the sump pit
• Accessible but undisturbed — the device should not be moved during the test period

Multiple Test Locations

EPA recommends testing each room used as sleeping quarters if those rooms are on different floors. For a typical single-family home, one test device on the lowest living level is the standard initial screen. For a more complete picture — particularly if you have a finished basement with a bedroom and a first-floor primary bedroom — placing devices in both locations simultaneously provides more information about exposure during sleep hours.

Multiple simultaneous tests do not need to be averaged — each result reflects the conditions in that specific room. Address any room reading above the EPA action level of 4.0 pCi/L.

Testing After Mitigation: Same Protocol

Post-mitigation test placement follows the same rules — lowest livable level, breathing zone, away from drafts and sump pits. Place the post-mitigation test device in the same room (or as close as possible to the same location) as the pre-mitigation test to enable a direct before/after comparison. This is not strictly required but simplifies interpretation.

Frequently Asked Questions

Should I test for radon in the basement or on the first floor?

Test in the basement if you have one — it is the lowest living level and where radon concentrations are highest. If the basement is unfinished and never occupied, you can also test on the first floor, but EPA recommends testing where people actually spend time. If you plan to finish the basement, test there first — before any renovation work that might seal in or redistribute radon entry pathways.

Can I put a radon test on my nightstand?

Yes — a nightstand is an excellent location if it is in the bedroom on the lowest sleeping floor. It is at breathing-zone height, in a room where you spend 7–8 hours nightly, and typically away from drafts and HVAC vents. Just confirm the nightstand is at least 12 inches from the wall and not adjacent to a window or exterior door.

My basement has multiple rooms — where should I put the test?

Choose a room you use or plan to use. If one room is a home office or bedroom and others are storage, test in the occupied room — that is where your actual exposure occurs. If all basement rooms are unfinished storage, test in the most central location accessible to you, then retest in the finished space after renovation if you later convert it to living use.