DIY Radon Testing: A Step-by-Step Guide

By Steve Crews · Last updated June 20, 2026

Short-term or long-term: choose before you buy

Before you order anything, pick a test type, because they work differently and each has a real use case.

A short-term test exposes a charcoal canister to your indoor air for two to seven days. Mail it back to the lab, and you get a result within a week or two from start to finish. This is the right starting point if you are buying or selling a home, have never tested before, or need an answer before an upcoming renovation.

A long-term test uses an alpha-track detector that stays in place for 90 days to 12 months. Because radon levels shift with seasons, weather, and how often you open the house, the longer exposure averages out those swings. If your short-term result comes back somewhere in the 2 to 4 pCi/L range, a long-term follow-up gives you more confidence before deciding whether to spend money on mitigation.

Short-term vs long-term radon tests has a full comparison. The short version: use a short-term test when you need speed, and consider a long-term test when you need accuracy.

Where to find a test kit

Check your state radon program first. Every state has one, and many offer kits for $5 to $15 through their health department website, which beats retail pricing considerably. The EPA maintains a directory of state radon contacts to point you in the right direction.

If your state program is out of stock or you want results faster, look for kits from labs certified by AARST-NRPP (the National Radon Proficiency Program), which is the leading national credential for radon measurement in the US. C-NRPP serves the same role in Canada. Certified kits from AccuStar (Air Chek) are widely available and consistently reliable. Their short-term charcoal canisters ship with a prepaid return envelope and registered lab analysis included. Check price on Amazon. If you decide to go straight to a long-term alpha-track kit, those are available from the same labs. Check price on Amazon.

Our best radon test kits roundup covers specific models, what certification marks to look for on the package, and how lab turnaround times compare.

Whatever kit you choose, make sure the price includes certified lab analysis. A bare detector with no lab affiliation is not a complete test.

Where to place the test

The EPA says to test the lowest level of your home that you use regularly. That usually means the basement if you spend time there. If your basement is pure storage and nobody occupies it, test the first floor instead. The point is to capture the air your household actually breathes, not simply the lowest possible point in the building.

Within that level, the placement details matter:

• Choose a room where someone spends time regularly: a bedroom, home office, or living area. Not a bathroom, kitchen, or laundry room.
• Place the detector at least 20 inches above the floor, at least 4 inches from exterior walls, and at least 3 feet from windows, exterior doors, and HVAC supply or return vents.
• Avoid spots with high humidity (near a sump pit, for example) and direct sunlight.
• A shelf, desktop, or bookcase at roughly chest height works well.

If you have a basement you regularly use and also want to know the reading upstairs, running one kit per level is reasonable. Two readings let you see whether the basement concentration is affecting the floor above.

Closed-house conditions

Short-term tests require what the EPA calls closed-house conditions throughout the entire test period: all exterior windows and doors stay closed except for normal entry and exit. Fans that bring in outside air should be off. Your furnace, central air conditioning, and ceiling fans can run normally, as long as they are not pulling fresh air in from outside.

Begin closed-house conditions at least 12 hours before you open the detector, and maintain them until you seal it at the end. If you crack the windows for an hour on a warm evening midway through a four-day test, the result is no longer valid.

Long-term tests do not require closed-house conditions. You live normally during the entire exposure period.

Placing and activating the test: step by step

1. Read the full kit instructions before touching the detector. Some charcoal canisters activate the moment you remove a foil seal; the clock starts at that moment.
2. Fill out the chain-of-custody form or register your kit number online if the lab uses a web portal. You will need your name, address, the start date and time, the room where you placed it, and the floor level.
3. Open or unseal the detector and set it in the chosen location.
4. Record the exact start time on the form.
5. Leave it completely undisturbed for the specified exposure window. That is genuinely all you do during the test.

There is nothing to check, adjust, or monitor while the test is running.

Closing and mailing the test

When the exposure window ends:

1. Record the end date and time on the chain-of-custody form.
2. Seal the detector as the instructions describe, usually replacing a cap or reapplying a foil cover.
3. Place the sealed detector and the completed form in the return mailer.
4. Drop it in the mail the same day you close the test, or the next morning at the latest.

Charcoal canisters absorb radon continuously, even after the test period ends. Delay between closing the detector and mailing it can inflate the result. If something comes up and you cannot mail it right away, refrigerate (do not freeze) the sealed canister until you can get it to a mailbox.

Reading your results

Most labs email results within a few days of receiving the kit. Your number arrives in picocuries per liter (pCi/L), the standard US unit for radon concentration. For reference, 1 pCi/L equals roughly 37 becquerels per cubic meter (Bq/m3), the unit used in Canada and most of the world.

Our how to read radon test results guide covers how to interpret the number in detail. The key benchmarks:

• Below 2 pCi/L: Considered low risk. The U.S. average indoors is about 1.3 pCi/L. No action is required, though the EPA notes that no level is entirely without risk.
• 2 to 4 pCi/L: The EPA recommends considering action, and a long-term test can help confirm whether the level is consistently in this range.
• 4 pCi/L and above: The EPA action level. The EPA and the U.S. Surgeon General both recommend fixing the problem.

For context, the WHO reference level is 100 Bq/m3 (about 2.7 pCi/L), and Health Canada’s guideline is 200 Bq/m3 (roughly 5.4 pCi/L). US guidance follows the EPA’s 4 pCi/L threshold, but those international benchmarks show that different authorities have landed on similar conclusions from the same evidence.

About 1 in 15 US homes exceeds the EPA action level. A high result is common enough that it should not come as a shock.

If your result is elevated

A reading at or above 4 pCi/L means the home needs mitigation, not that you are in immediate danger. The standard fix is a sub-slab depressurization system installed by an AARST-NRPP certified contractor. These systems place a fan and pipe below the foundation slab to draw radon out before it enters living space and vent it harmlessly above the roofline. A properly designed system can reduce indoor radon by 90 percent or more, bringing most homes well under the action level.

Get at least two quotes from certified mitigators, and ask each one which entry points they plan to address and what their post-installation guarantee looks like. After installation, retest within 24 hours to 30 days. The system is only verified working once a measurement confirms it.

If your result landed in the 2 to 4 pCi/L range and you are not sure whether to mitigate, a long-term test will give you a more reliable annual average to base the decision on.

FAQ

How long does a DIY radon test take from start to result? A short-term charcoal test typically stays in the home for 48 to 96 hours, depending on the kit. Add a few days for mail transit and lab processing, and you have a result within one to two weeks total. Long-term alpha-track tests stay in place 90 days to a year, with lab processing added after that.

Do I have to keep windows closed for the entire test? For short-term tests, yes. The EPA requires closed-house conditions for at least 12 hours before you start the test, and for the full duration. Normal HVAC use is fine. Opening exterior windows or doors for ventilation, beyond routine entry and exit, compromises the result and means you should restart.

What if my radon result seems too high or surprisingly low? Run a second short-term test under the same conditions, or follow up with a long-term test for a more stable average. Radon levels fluctuate naturally with season, weather, and occupancy patterns, so a single short-term reading is a useful starting point but not necessarily your permanent number.

Can I test in summer or does it have to be winter? Short-term testing is easier in cooler months when the house stays closed naturally. If you have central air conditioning and can keep exterior openings shut, summer testing works fine. If you rely on open windows to stay comfortable, wait for fall. Winter and early spring tend to show the highest concentrations because homes are sealed and the pressure difference between indoor air and soil gas is greatest.