What Should You Know About Radon Testing Before Purchasing a Property?

A home inspection can tell you about the roof, the wiring, and the boiler. It cannot see the one hazard that is colorless, odorless, and rising from the ground beneath the floor. Radon is a radioactive gas that seeps from soil into buildings, and the only way to know how much your future home has is to measure it. Buyers often skip the test because the sale feels rushed, or because the house looks perfectly healthy. So what should you know about radon testing before purchasing a property? You need to know what number counts as high, how the test must be done to be valid, how to read a result, and what to do if it fails. This guide covers each step. You will find a quick answer, a results table, a test setup table, a purchase timeline, a negotiation checklist, and a short FAQ.

What Should You Know About Radon Testing Before Purchasing a Property?

Test the lowest livable level of the home, using a short-term test under closed-house conditions, and compare the result with your local action level. If the result is high, confirm it with a second test, then negotiate mitigation with the seller or adjust your offer. Hire a certified tester where your area requires or recommends one.

How Do You Read the Number?

Radon is measured in picocuries per liter of air (pCi/L), and the EPA action level is 4.0 pCi/L, though no level is known to be completely safe. One pCi/L equals about 37 Bq/m³, so the EPA level is roughly 148 Bq/m³. The World Health Organization recommends a lower action level of 2.7 pCi/L, or 100 Bq/m³.

Result (pCi/L)	Meaning	Suggested Next Step
Below 2	Relatively low	Retest every few years and after renovations
2 to 4	Below the EPA action level, but not risk free	Consider fixing, especially for households with children or smokers
4 to 8	At or above the EPA level	Follow up with another short-term or a long-term test
Above 8	Clearly elevated	Confirm quickly and plan mitigation

Local rules may use different numbers, so check your health authority.

How Should the Test Be Set Up?

Requirement	Why It Matters
Test the lowest livable level	Radon is usually highest in the lowest level suitable for occupancy
Closed-house conditions	Keep windows and exterior doors shut, and begin at least 12 hours before and continue during a short-term test
Minimum duration	A 48-hour minimum short-term test is typical for real estate transactions
Do not move the device	Disturbing it can invalidate the result
Normal heating and cooling	Keeps conditions realistic
Independent tester	Reduces the risk of a biased result

Open windows or fans that draw outside air can dilute the reading and understate the risk.

What Does a Short-Term Test Miss?

A short-term test gives a snapshot of the test period, while a long-term test gives an annual average. A winter test may read higher than the yearly average, and a summer test lower. Treat a single number near the limit as a prompt to confirm, not as a verdict. Radon also varies from house to house, so a neighbor’s result tells you little about yours.

What Does the Purchase Timeline Look Like?

Stage	Action
Before the offer	Ask whether a radon test has been done and request the report
In the offer	Add a radon testing clause with a clear deadline and action level
During the inspection period	Run the short-term test under closed-house conditions
After a high result	Confirm with a second test
Before closing	Agree on mitigation, a price change, or a repair credit
After moving in	Retest after mitigation and after major renovations

How Should You Negotiate a High Result?

If the test is 4 pCi/L or greater, the EPA recommends that buyers negotiate with the seller to install a mitigation system that brings the level below 4 pCi/L. Ask for the work to be done by a qualified professional, with a post-installation test and warranty details in writing. Most elevated homes can be fixed, so a high result should lead to a plan rather than automatically ending the deal.

Frequently Asked Questions

Can a vacant house be tested?
Yes. Closed-house conditions are often easier to maintain in an empty home.

Do new homes need testing?
Yes. Radon depends on the ground and the building, not on age.

Does the test replace a home inspection?
No. It adds a separate measurement the inspection does not cover.

Bottom Line

Radon testing is quick and cheap compared with the price of a home. Test the lowest livable level under proper conditions, treat borderline results as a reason to retest, and write a testing clause into your offer. If the number is high, negotiate a fix before you close.

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