How to Test for Radon in Your Home

Testing for radon in your home is a straightforward process that every homeowner should complete at least once — and repeat every two years. Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It is colorless, odorless, and tasteless, making testing the only way to know whether levels in your home pose a health risk. The U.S. Environmental Protection Agency (EPA) recommends that all homes below the third floor be tested, regardless of foundation type, region, or construction age. The EPA action level is 4 picocuries per liter (pCi/L) — at or above that threshold, the agency recommends radon mitigation to reduce your home’s radon concentration. The process is not complicated: you can perform a reliable initial screening yourself with a $15–$30 test kit, or hire a certified professional for a more comprehensive assessment. This guide walks through every step — from choosing the right test type to interpreting your results and deciding what to do next.

Step-by-Step: How to Test for Radon in Your Home

Step 1: Choose Your Test Type

Two primary test types are available for residential radon testing:

• Short-term charcoal canister (2–7 days): The most common DIY option. An activated charcoal canister passively absorbs radon decay products over the exposure window. After the test period, you mail the sealed canister to an accredited laboratory. Results are typically returned within 3–10 business days. This is the standard choice for initial screening and real estate transactions.
• Long-term alpha track detector (90 days to 1 year): An electret or alpha track film records cumulative radon exposure over an extended period. This method provides a more accurate picture of your annual average radon exposure, which better reflects real health risk than a 2–7 day snapshot. The EPA recommends a long-term test when a short-term result falls between 4–8 pCi/L.

Both types require sending to an EPA-listed accredited laboratory. Look for kits certified through the National Radon Program Services (NRPS) or the National Radon Proficiency Program (NRPP).

Step 2: Purchase or Obtain a Test Kit

Radon test kits are available at hardware stores (Home Depot, Lowe’s), home improvement retailers, online (Amazon, Radon.com, Kansas State University NRPS), and — often for free or minimal cost — through your state radon program. Before purchasing, check your state health department’s radon program website. Many states in EPA Zone 1 — including Pennsylvania, Colorado, Minnesota, Ohio, Iowa, Montana, and North Dakota — offer subsidized or free kits through county health departments or conservation districts.

A standard DIY short-term kit costs $15–$30 and includes the canister, instructions, prepaid return envelope, and laboratory analysis fee.

Step 3: Prepare Your Home — Closed-House Conditions

Before and during the test period, your home must maintain closed-house conditions. This means:

• Keep all windows and exterior doors closed, except for normal entry and exit
• Do not operate whole-house fans or window fans that bring in outside air
• Normal HVAC operation (heating and air conditioning) is acceptable
• Closed-house conditions must be maintained for at least 12 hours before placing the canister and throughout the entire test period

Failure to maintain closed-house conditions is the most common source of inaccurate short-term test results. Natural ventilation dilutes indoor radon and will produce a falsely low reading.

Step 4: Place the Test Kit in the Correct Location

Placement is critical. Follow these EPA-recommended guidelines precisely:

• Level: Place the detector in the lowest livable level of your home — typically the basement if you use it regularly (even occasionally for laundry or storage counts). If you have no basement, use the first floor.
• Height: Place the canister 20 inches (50 cm) to 6 feet above the floor.
• Away from drafts: Keep the canister at least 4 inches from walls and away from windows, doors, exterior walls, sump pumps, and HVAC vents.
• Away from high humidity: Do not place in bathrooms or kitchens. Humidity affects activated charcoal performance.
• Not disturbed: Place the canister where it will not be moved, covered, or handled during the test period. Do not place it in closets or storage areas with significant airflow variation.

Step 5: Leave the Kit Undisturbed for the Full Test Period

For short-term charcoal tests: leave the canister in place for exactly 48–96 hours (2–4 days) — or up to 7 days per your kit instructions. Note the exact start time and date on the packaging. Maintain closed-house conditions throughout. Do not open the canister.

For long-term alpha track tests: leave the detector in place for 90 days to one year. Closed-house conditions are not required for long-term tests — the extended exposure period accounts for seasonal variation.

Step 6: Seal and Mail the Test Kit to the Laboratory

At the end of the test period, note the exact end time on the packaging. Seal the canister immediately — activated charcoal continues to absorb after the test period if left open. Mail within 24–48 hours using the prepaid return envelope included with the kit. Delays between test completion and mailing can affect result accuracy.

Step 7: Interpret Your Results

The laboratory will return your results by mail or online (most kits now provide online results access).

Result (pCi/L)	Risk Level	Recommended Action
Below 2 pCi/L	Low	No immediate action required; retest every 2 years
2–3.9 pCi/L	Moderate (below EPA action level)	Consider long-term test to confirm; mitigation optional but reasonable
4–7.9 pCi/L	Elevated — EPA action level	Conduct follow-up long-term test; mitigate if confirmed above 4 pCi/L
8–19.9 pCi/L	High	Mitigate within a few months; no need to wait for long-term confirmation
20 pCi/L or above	Very High	Mitigate as soon as possible — within weeks

The average U.S. indoor radon level is approximately 1.3 pCi/L. The EPA action level of 4 pCi/L is roughly 200 times the concentration found in outdoor air (approximately 0.4 pCi/L average). The World Health Organization (WHO) recommends a national reference level of 2.7 pCi/L, lower than the EPA threshold.

Step 8: Take Action Based on Results

If your short-term result is below 4 pCi/L, retest in two years. If your result is 4 pCi/L or higher, contact a certified radon mitigation contractor. NRPP- and AARST-certified contractors can diagnose your home, design a mitigation system, and install it — most in a single day. After installation, a post-mitigation test within 24–48 hours confirms system effectiveness. EPA data shows that properly designed sub-slab depressurization systems reduce radon levels by up to 99% in most homes.

Should You Test Yourself or Hire a Professional?

For most homeowners conducting a routine baseline test, a DIY kit is entirely appropriate. The laboratory analysis is the same — only the chain of custody and site protocol documentation differ.

Hire a certified radon measurement professional (NRPP-listed) when:

• You are buying or selling a home and need certified documentation
• The result will be used in legal, real estate, or insurance proceedings
• You want hourly-resolution data from a continuous electronic monitor
• You are managing a multi-unit residential or commercial building
• A prior DIY test produced a result you believe may be inaccurate due to testing conditions

EPA Radon Zones and Why Location Matters for Testing

The EPA’s radon zone map divides U.S. counties into three categories based on predicted indoor radon potential. Zone 1 counties (highest risk) include much of Pennsylvania, Colorado, Iowa, Minnesota, South Dakota, North Dakota, Montana, Ohio, Kentucky, and Wisconsin. Zone 2 counties are moderate risk. Zone 3 counties have lower predicted levels, though individual homes in any zone can exceed 4 pCi/L.

Even in Zone 3 states, testing is essential — radon levels are determined by local geology, soil permeability, and home construction, not ZIP code alone. In a 2022 EPA analysis, approximately 1 in 15 U.S. homes was estimated to have radon levels at or above the action level of 4 pCi/L. Homes in Zone 1 counties have significantly higher rates.

State radon programs provide county-level data, contractor directories, and often free or subsidized test kits. Contact your state health department’s radon or environmental health division for local resources before purchasing a kit.

Frequently Asked Questions — How to Test for Radon

Get a Free Radon Quote

Already have your results? Or want help choosing the right test? Connect with a certified radon professional in your area — no obligation, no pressure.