Radon testing when selling a home in NH

If you’re listing a house in Nashua, Manchester or a nearby town, radon will probably come up. Here’s what New Hampshire law asks of sellers, how a real-estate radon test is run, and how to keep a high number from derailing the deal.

What New Hampshire law requires

Before a purchase and sale agreement is signed for property with a building on it, the seller or the seller’s agent must give the buyer a written notice covering radon, arsenic, lead, PFAS and flood risk. The buyer signs a copy to acknowledge it (RSA 477:4-a). The radon part of the required wording reads:

“Radon, the product of decay of radioactive materials in rock, may be found in some areas of New Hampshire. Radon gas may pass into a structure through the ground or through water from a deep well. Testing of the air by a professional certified in radon testing and testing of the water by an accredited laboratory can establish radon’s presence and equipment is available to remove it from the air or water.”

The statute requires the notice. It doesn’t order a test. It also says a seller isn’t liable for failing to give the notice. If the home is on a private well, a separate seller disclosure for one- to four-family homes covers the water supply system, including the date of the most recent water test (RSA 477:4-d).

This is a plain-language summary, not legal advice. Your agent or attorney can tell you how it applies to your sale.

Why test before you list

The EPA says it’s better to fix a radon problem before the home goes on the market, because you have more time to deal with it (EPA). Testing early also means:

• No surprise in the inspection window. You’ll know your number before a buyer does.
• A record buyers can see. The EPA suggests saving your test results and any mitigation details, which it says “could be a positive selling point” (EPA).
• Room to fix it on your schedule. If the result is high, you can get quotes and a post-mitigation test without a closing date bearing down on you.

According to the EPA guide, a buyer may still ask for a new test if your last one isn’t recent (the guide’s example is within two years), if you’ve renovated since, or if they plan to use a lower level of the house that you didn’t (EPA).

How a real-estate radon test works

Real-estate tests are short-term tests, because nobody can wait months. NH DHHS defines short-term tests as running 2 to 90 days (NH DHHS). The EPA says every real-estate test should run at least 48 hours. Some devices need longer (EPA).

The EPA describes three acceptable short-term approaches for a sale. In each one, it recommends fixing the home if the average is 4 pCi/L or higher (EPA):

1. Two passive tests at the same time, for at least 48 hours.
2. Two identical tests, one after the other.
3. A continuous radon monitor, for at least 48 hours.

NH DHHS describes the side-by-side version: two kits placed at least 4 inches apart, with the results averaged, and a retest if the two disagree a lot (NH DHHS). The EPA notes that simultaneous tests improve precision, while back-to-back tests better reflect a seasonal average (EPA).

Getting the timing and conditions right

• Closed-house conditions. For tests of 2 to 4 days, the EPA calls for keeping windows and outside doors closed, except for normal entry and exit, for 12 hours before and throughout the test (EPA). NH DHHS gives the same 12-hour rule (NH DHHS).
• Watch the weather. The EPA says not to run tests shorter than four days during severe storms or periods of high winds. NH DHHS says to avoid testing when winds are over 30 mph (EPA, NH DHHS).
• Placement. Test in the lowest level that is (or could be) used regularly. Place the device at least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls (EPA).
• Season. NH DHHS notes radon tends to run higher in colder months, and suggests retesting in winter if a test was done in warmer months (NH DHHS).
• Turnaround. The free state kit is a good way to get a first look early. NH DHHS’s kit instructions say results come by mail in about two weeks (NH DHHS). That can be too slow once you’re under contract. The EPA notes you can ask a lab for expedited service (EPA).

If the house already has a radon system, the EPA says the fan should be running during the test (EPA).

Keep the test credible

Buyers want to trust the number. The EPA lists ways to guard against interference during a sale. These include motion detectors, tamper-proof seals on windows, recording temperature and barometric pressure, and a non-interference agreement signed by the seller or occupant (EPA). Certification isn’t required for radon testing in New Hampshire, but NH DHHS recommends a nationally certified measurement professional, especially for a real-estate transaction (NH DHHS). You can check certifications on the NRPP site.

Reading the result

• 4 pCi/L or higher (average): the EPA recommends fixing the home.
• Between 2 and 4 pCi/L: the EPA suggests considering a fix.
• Close to 4: the EPA guide explains that an average of 4.1 pCi/L means there is about a 50% chance the true year-round average is above 4, and about a 50% chance it is below (EPA).

For context, the EPA puts the average indoor level at about 1.3 pCi/L and outdoor air at about 0.4 pCi/L (EPA).

If the number comes back high

The EPA says that when an elevated level turns up during a sale, the buyer and seller should discuss the timing and cost of radon reduction. It also says to get estimates from one or more qualified mitigators, and that most homes can be fixed for about the same cost as other common home repairs (EPA). The EPA says that in most cases, a system with a vent pipe and fan is used. It does not recommend sealing cracks as the only fix (EPA). After a system goes in, retest to confirm it worked. In New Hampshire, radon-in-air mitigation installers must be nationally certified (NHDES). Read more in our mitigation guide.

The notice in RSA 477:4-a also mentions radon in water from a deep well. If your home has a private bedrock well, see our notes on radon in well water.

Seller checklist

1. Test before listing, or at least before you accept an offer. A free state kit works for a first look.
2. If you have time, follow up with a two-device or continuous-monitor test that meets the EPA’s real-estate protocol.
3. Keep every report, including lab results, dates and device locations.
4. If the average is 4 pCi/L or higher, get a written mitigation quote that includes a post-mitigation test.
5. Have the RSA 477:4-a notice signed before the purchase and sale agreement.

Selling in Nashua? See our Nashua home-sale page and the radon FAQ.