Radon Testing in New Hampshire: Buyer's Guide (2026)

Quick answer: Yes — you should test for radon before buying almost any home in New Hampshire. The state has some of the highest radon levels in the country, averaging around 8.98 pCi/L indoors, more than double the EPA's 4.0 pCi/L action level. A short-term radon test during your home inspection costs about $150–$250, and if levels come back high, a mitigation system runs roughly $800–$2,500.

Radon is a colorless, odorless radioactive gas produced as uranium in soil and rock breaks down. You can't see it, smell it, or taste it — the only way to know your level is to test. In New Hampshire, that matters more than almost anywhere else, and skipping radon testing in New Hampshire is one of the few home-buying shortcuts we'll always tell a client not to take.

Why does New Hampshire have such high radon levels?

It comes down to geology. New Hampshire isn't nicknamed the Granite State by accident — the same uranium-bearing granite bedrock that gives us our scenery also releases radon gas as it decays. That gas seeps up through cracks in slabs, around sump pits, and through dirt crawl-space floors, then concentrates inside the tight, well-insulated homes we build for cold winters.

The numbers back it up. New Hampshire's average indoor radon reading is about 8.98 pCi/L, and communities in southeastern and eastern New Hampshire tend to see the highest concentrations. Rockingham County — home to Salem, Derry, Londonderry, Windham, and the Seacoast — along with Carroll and Coos counties, has several towns where more than half of the homes tested came back elevated. If you're buying anywhere in our service area, assume radon is a real possibility until a test proves otherwise.

What is a safe radon level when buying a home in NH?

The EPA sets 4.0 pCi/L as the action level: at or above that reading, you should install a mitigation system to bring the number down, ideally under 2.0 pCi/L. There's no truly "safe" level of radon — the risk simply drops as the number drops — but 4.0 is the industry line for when action is expected. Understanding radon levels in New Hampshire is important because a reading that would be alarming elsewhere is common here, and it's very fixable.

Should I get a radon test during my home inspection?

Almost always, yes. A short-term radon test is easy to add to your standard home inspection, and it's the cheapest insurance in the whole transaction. On the inspections we coordinate across southern New Hampshire, we routinely recommend adding a radon-in-air test to the inspection order so the result lands inside your inspection contingency window. That timing gives you room to negotiate mitigation with the seller if the number comes back high. The NH Department of Environmental Services recommends using a nationally certified radon measurement provider, and NHDES even offers free radon test kits for homeowners who want to confirm a result later.

How much does radon testing and mitigation cost in New Hampshire?

A professional short-term air test during your home inspection typically costs $150–$250. If mitigation is needed, a standard sub-slab depressurization system — a fan and vent pipe that pulls radon out from under the foundation and exhausts it above the roofline — usually falls in the $1,000–$1,500 range, with more complex homes running up toward $2,500. Since January 1, 2015, New Hampshire has required radon mitigation designers and installers to be nationally certified, so ask for that credential before hiring anyone. It's a one-time fix that permanently lowers the health risk and is an easy line item to ask a seller to cover.

What about radon in well water?

Here's the New Hampshire wrinkle most buyers miss: radon shows up in private well water too, not just the air. It's a separate test from the general water panel. NHDES uses an advisory level of 2,000 pCi/L for radon in water. Wells testing at or above 10,000 pCi/L should be treated regardless, and wells between 2,000 and 10,000 pCi/L should be treated if the home's air reading also exceeds 4.0. As a rule of thumb, about 10,000 pCi/L of radon in water adds roughly 1 pCi/L to the air. If you're already testing a private well — and in rural NH you almost certainly should be — ask the lab to add radon, uranium, and gross alpha to the panel.

What happens if the radon test comes back high?

Don't panic — a high reading is a negotiation point, not a dealbreaker. NHDES recommends at least two tests, ideally a month apart, before making a treatment decision, though the transaction timeline often means you'll act on the inspection-period short-term test. From there you have options: ask the seller to install a certified mitigation system before closing, request a credit to cover it yourself, or split the cost. Because mitigation is affordable and effective, high radon rarely kills a deal — it just needs to be handled. This is exactly the kind of moment where an experienced local agent earns their keep.

Related reading

If radon is on your inspection list, these guides pair naturally with it: our New Hampshire home inspection walkthrough, our guide to well water testing when buying a NH home, and — if you're eyeing an antique — buying an old colonial home in New Hampshire.

Testing radon is a small step with a big payoff

New Hampshire's median single-family home sold for about $575,000 as of June 2026 (NH Association of Realtors), and homes are still moving in roughly a month. In a market moving that fast, it's tempting to waive contingencies to win a bid — but a $200 radon test protects both your health and your investment. Whether you're buying in Bedford, Manchester, Nashua, or out toward the Seacoast, build radon into your inspection plan. Ready to make a move? Start with our home buying guide, browse our buyer resources, or reach The Phinney Team through teamphinney.com and we'll help you line up trusted, certified inspectors across southern New Hampshire.

Sources: U.S. EPA — Radon and the NH DHHS Radon Tracking Program.

Frequently asked questions about radon testing in New Hampshire

Is radon testing required when buying a home in New Hampshire?

No, radon testing isn't legally required to buy a home in New Hampshire, but it's strongly recommended and easy to add to your home inspection. Given how high radon levels in New Hampshire run, most buyers and lenders treat it as a standard part of due diligence rather than an optional extra.

Who pays for radon mitigation, the buyer or seller?

It's negotiable. When a radon test comes back above 4.0 pCi/L during the inspection period, buyers commonly ask the seller to install a certified mitigation system or provide a closing credit. In a competitive market the buyer sometimes absorbs the cost, but it's almost always on the table for discussion.

How long does a radon test take?

A short-term radon test typically runs 48 hours to a few days, which fits neatly inside most New Hampshire inspection contingency windows. Long-term tests spanning 90 days or more give a more accurate annual average, but the short-term test is what's used during a home purchase.

Can I test for radon myself?

Yes. DIY kits are inexpensive and NHDES offers free radon test kits, which are great for peace of mind after you move in. During a purchase, though, most buyers use a certified professional so the result is documented and credible if it becomes part of an inspection negotiation.