Radon test results explained: what your number means
If your inspection included a radon test, your report has a number on it, often something like “4.6 pCi/L.” Here’s what that number means, when it matters, and what happens if it’s high.
What radon is
Radon is a natural radioactive gas that comes from uranium breaking down in soil and rock. You can’t see or smell it. It moves up from the ground and can collect inside homes, especially in basements and lower levels. Long-term exposure raises the risk of lung cancer, which is why the EPA recommends testing homes.
How to read your number
Results are usually reported in picocuries per liter of air, written pCi/L. A home inspection test usually runs for at least two days, and the report gives the average level over that time.
- 4.0 pCi/L or higher: the EPA’s action level. The EPA recommends fixing the home.
- 2.0 to 4.0 pCi/L: the EPA suggests considering a fix, since there’s no known safe level of radon.
- Below 2.0 pCi/L: lower risk. For comparison, the average indoor level in American homes is about 1.3 pCi/L, and outdoor air averages about 0.4 pCi/L.
Property Made Clear turns inspection reports into a calm, plain-English summary, sorted by what to handle first.
How high radon is fixed
The most common fix is a radon mitigation system. A contractor installs a pipe that draws air from beneath the foundation and a fan that vents it outside above the roofline, so radon is pulled away before it can enter the home.
Installation usually takes about a day. Costs vary with the home’s size and foundation type. Massachusetts’ public health guidance, for example, puts most systems around $1,000 to $1,500. A local quote will give you the real number for your home.
After installation, the home should be retested to confirm the level has dropped. A good contract should guarantee a result below 4.0 pCi/L, and ideally below 2.0.
What it means when you’re buying
A high radon result is common, and it’s usually handled as part of the repair negotiation. Buyers often ask the seller to install a mitigation system before closing or to offer a credit toward one.
Talk with your agent about what’s typical in your area, get a quote from a certified radon mitigation contractor, and plan to retest after the system is installed.
This guide is general information, not professional advice. For anything specific to your home, talk with your home inspector or a licensed professional.