Radon: Testing, Levels and Mitigation

How to test your home for radon, read the result against EPA levels, and understand what a mitigation system does and who should install it.

Radon is a naturally occurring radioactive gas released from rock and soil, and it has no taste, odor or color. EPA states plainly that testing is the only way to know your level of exposure, and that all homes should be tested. CDC describes radon as the second leading cause of lung cancer after smoking. This hub covers testing, reading the number, and fixing a high result.

Testing

A short-term kit answers the question in days; a long-term kit, running more than 90 days, describes what you actually breathe across seasons. Closed-house conditions are what make a short-term result meaningful, so follow the instructions on your own kit exactly. Our radon test kit guide covers choosing and running one.

Reading the result

EPA recommends homes be fixed if the radon level is 4 pCi/L or more. Because there is no known safe level of exposure, EPA also recommends considering a fix between 2 pCi/L and 4 pCi/L. For context, the average indoor level in American homes is about 1.3 pCi/L, and outdoor air averages about 0.4 pCi/L. Our guide to radon levels works through each band.

Mitigation

The standard fix is sub-slab depressurization: a pipe sealed into the floor slab, a fan drawing soil gas from beneath it, and a discharge above the roofline. CDC advises contacting a qualified professional to install a radon reduction system if your level is at or above 4 pCi/L. Sealing cracks helps but is not a complete fix on its own. See how a radon mitigation system works.

What it costs

Published radon cost figures frequently bundle testing with mitigation, which makes quotes look wrong in both directions. Our cost guide separates them and names the scope of every figure it quotes, and the Radon Mitigation Cost Estimator scores how complex your particular job is likely to be.

Timing matters

Test before finishing a basement rather than after, because converting a storage cellar into a bedroom changes your exposure substantially. Retest every couple of years, and after any foundation work, new slab or mitigation system installation.

Start with these guides

Radon Test Kit: How to Test Your Home and Read the Result How to choose and use a radon test kit: short-term versus long-term kits, the closed-house conditions that make a result valid, where in the house to place it, and what EPA says each result means.
How to Test for Radon: Kits, Placement and Results Choosing between short and long-term radon testing, placing the detector where the result means something, and what to do with the number you get.
Radon Levels Explained: What Your pCi/L Result Means What your radon reading means: EPA’s action level, the consider-fixing band, the national average, and why there is no level that counts as safe.
Radon Mitigation System: How It Works and What to Expect How a radon mitigation system works, which design suits your foundation, what a certified installer should do, and how to confirm the system is actually reducing your level.
Radon Mitigation System Cost: What Drives the Price What a radon mitigation system costs, which factors move the quote, why published ranges often bundle testing with the fix, and how to compare quotes line by line.

Tools for this topic

Radon Mitigation Cost Estimator – scope and complexity, not an invented price
Basement Dry-Up Plan Builder – where radon fits in your plan
Basement Safety and Maintenance Checklist – seasonal retest reminders

Latest Radon guides

New guides are added as they pass our fact-check. Browse everything in Radon, or get new guides by email.

Sources we rely on

Frequently asked questions

What radon level is dangerous?

EPA recommends homes be fixed at 4 pCi/L or higher, and considering a fix between 2 and 4 pCi/L. Because there is no known safe level, lower is always better.

How do I test for radon?

Use a short-term or long-term test kit placed in the lowest level of the home that you use regularly, following the closed-house conditions on the kit. EPA states testing is the only way to know your level.

Can I install a radon mitigation system myself?

Sealing and testing are homeowner tasks. CDC advises contacting a qualified professional to install a radon reduction system when your level is at or above 4 pCi/L, because the design decides whether it works.

Does sealing cracks reduce radon?

It helps, and CDC suggests sealing cracks and increasing ventilation even below 4 pCi/L. It is not a complete fix on its own, because concrete keeps cracking and penetrations are easy to miss.

Do I need to test if I have no basement?

Yes. CDC states radon can build up in any home or building, whether it has a basement, is sealed or drafty, or is new or old.