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Where should a radon test be placed?

By Radon411 Editorial TeamUpdated How we research

Short answer

Place a radon test in the lowest lived-in level of the home, in a room used regularly such as a living room or bedroom, not the kitchen or bathroom. Set it at least 20 inches above the floor where it won't be disturbed, away from drafts, high heat, high humidity and exterior walls.

Next step: pick the right test for your home. Which test to use

The lowest lived-in level is the lowest floor used regularly: the basement if it is frequently used, otherwise the first floor. A crawl space is not a lived-in level, so a home test goes in the living space above it.

Some spots give misleading readings. Do not test in a closet, stairway, hallway or crawl space, or in an enclosed area of high humidity or high air velocity, such as a kitchen, bathroom, laundry room or furnace room. Follow your device's own instructions as well.

Placement is only half of a valid test. Every radon test should run for a minimum of 48 hours, and for a short test of 2 to 4 days, start at least 12 hours before it begins and last the whole test. Do not move or disturb the device until the test is over.

What to do next: pick the room, set the device out as its instructions describe, and record the start date and time. When the result comes back, read it with the interpreter, and if it is high, plan a follow-up test.

Placement rules at a glance

Where you put a radon test matters as much as which test you buy. The aim is a reading from the level you use where radon is usually highest, with nothing in the room skewing it.

Where to put a radon test, and where not to
RuleDoDon't
LevelThe lowest lived-in level: the basement if it is frequently used, otherwise the first floorAn unused level below the one you live on, unless you plan to use it
RoomA room used regularly, such as a living room, playroom, den or bedroomThe kitchen or bathroom
HeightAt least 20 inches above the floorOn the floor
SpotWhere it won't be disturbedIn drafts, high heat or high humidity, or against an exterior wall
Spaces to avoidAn ordinary roomA closet, stairway, hallway or crawl space, or a laundry or furnace room

Why the lowest lived-in level

Radon comes up from the soil, so levels are usually higher in basements, cellars and living spaces in contact with the ground. If your living patterns change and you begin using a lower level, such as a basement, retest on that level.

Cross-section drawing of a house with a basement and a crawl space, numbered at the seven ways EPA lists for soil gas to get in: cracks in solid floors, construction joints, cracks in walls, gaps in suspended floors, gaps around service pipes, cavities inside walls, the water supply.
Read this figure as text
House in cross-section showing where soil gas entersGround levelSoil and rockBasementSolid floorCrawl spaceSuspended floor1234567
  1. Cracks in solid floors
  2. Construction joints
  3. Cracks in walls
  4. Gaps in suspended floors
  5. Gaps around service pipes
  6. Cavities inside walls
  7. The water supply
Soil gas enters at or near the lowest level of a house, which is why the test goes there.

In a home sale, the rule shifts slightly: test in the lowest level that could be used regularly, finished or not, because a buyer may choose to live in a lower area than the seller did.

Placement by type of home

Where the test goes in common layouts
HomeWhere to test
Basement used as living spaceIn a regularly used basement room, such as a family room or bedroom
Unfinished basement you don't useOn the first floor, unless you plan to use the basement; in a sale, test the basement a buyer could use
Split-level homeThe lowest level you use regularly
Slab-on-grade or crawlspace homeOn the main floor, in a living room or bedroom; never in the crawlspace itself
Apartment below the third floorIn a main room of the unit

For a home with no basement, see radon testing without a basement.

Conditions during the test

A good spot can still give a bad reading if the house is aired out. For a , keep windows and outside doors closed as much as possible during the test, and for a test of 2 to 4 days, start at least 12 hours before it begins. Heating and air-conditioning that recirculate air may run; fans that bring in outside air should not.

  1. Close up

    Windows and outside doors closed at least 12 hours before a 2 to 4 day test, and kept closed except for normal entry and exit.

  2. Place and record

    Set the device in the chosen room, at least 20 inches up, and note the start date and time.

  3. Leave it alone

    Do not move or disturb the device for the whole test, which should run a minimum of 48 hours.

  4. Finish and send

    Record the stop time, reseal the kit and send it to the lab right away.

Two devices, or a monitor

Sometimes two devices are used. Two short-term tests can be placed side by side, four inches apart, and their results used together to decide whether to fix the home; two tests taken at the same time improve the precision. A continuous monitor, which measures and records radon through the whole test, is placed by the same rules and run for at least 48 hours.

EPA's three short-term radon testing options for a real estate transaction: two tests at the same time, one test then a second, or a continuous monitor, each for at least 48 hours, with what to do after each.
Read this figure as text

If you are testing in a real estate transaction and you need results quickly, any of the following three options for short-term tests are acceptable in determining whether the home should be fixed.

  1. Option 1. Two tests at the same time

    Passive

    Take two short-term tests at the same time in the same location for at least 48 hours.

    What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

    Two tests taken at the same time (simultaneous) would improve the precision of this radon test.

  2. Option 2. One test, then a second

    Passive

    Take an initial short-term test for at least 48 hours. Immediately upon completing the first test, do a second test using an identical device in the same location as the first test.

    What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

    One test followed by another test (sequential) would most likely give a better representation of the seasonal average.

  3. Option 3. A continuous monitor

    Active

    Test the home with a continuous monitor for at least 48 hours.

    What to do nextFix the home if the average radon level is 4 pCi/L or more.

    Both active and passive devices may have features which help to prevent test interference.

Any real estate test for radon should include steps to prevent or detect interference with the test device. Your state radon office can help you decide which option is best.

The three short-term testing options for a home sale: two tests at once, one test after another, or a continuous monitor.

Questions about where to place a radon test

Should a radon test be placed in the basement?

If the basement is used regularly, yes. If it is not, test the first floor, unless you plan to use the basement, in which case test there.

Can I put a radon test in the kitchen or bathroom?

No. Avoid kitchens and bathrooms, along with laundry and furnace rooms: they are enclosed areas of high humidity or high air velocity.

How high off the floor should a radon test be?

At least 20 inches above the floor, where it won't be disturbed.

Can I place a radon test near a window or outside wall?

No. Keep it away from drafts, high heat, high humidity and exterior walls.

Where do you put a radon test in a split-level home?

On the lowest level you use regularly. In a sale, test the lowest level a buyer could use regularly, finished or not.

Should I test in a crawlspace?

No. A crawl space is on the list of places not to test; put the device in the living area above it.

Where should two test kits go?

Side by side, four inches apart, in the same location, so the two results can be used together.

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