Radon Testing & Mitigation During an NH Home Sale: A Guide for Buyers, Sellers, and Realtors

Roughly one in three New Hampshire homes has indoor radon at or above the EPA action level. That single fact is why radon testing is part of nearly every NH real estate transaction — and why a high radon result mid-deal is one of the most common avoidable causes of a transaction stalling. It does not have to be.

This guide explains how radon testing and mitigation fit into an NH home sale: who tests, who pays, what timelines look like, what the numbers mean, and how to keep a transaction on track when radon enters the conversation. It is written by AARST/NRPP-certified mitigators who do this work daily, on transaction timelines, across Southern, Central, and Coastal NH.

Why radon is part of nearly every NH home sale

Two reasons. First, NH has higher-than-average radon: the granite bedrock that defines the state's geology is also a meaningful source of radon gas in homes. Second, radon is invisible to a casual walkthrough — a buyer cannot see or smell it, and the seller may have lived comfortably in the home for years while levels were elevated. The standard inspection contingency, which most NH purchase agreements include, is the mechanism by which the buyer (or buyer's agent) commissions a short-term radon test as part of due diligence.

This is true for new construction, recently renovated homes, and historic homes alike. A modern, well-built home is not exempt; in fact, the air-tightness that makes a new build energy-efficient can also concentrate radon.

How transaction-grade radon testing works

Real-estate radon tests are not casual. They follow ANSI/AARST MAH-2019, the consensus protocol for measurement during real estate transactions. The protocol exists because conditions during a test materially affect the result, and a non-protocol test will not hold up under inspection-contingency review. Key points:

• Closed-house conditions. Windows and exterior doors stay closed for 12 hours before and during the test, beyond normal entry/exit. HVAC operates normally. This is the standardized condition under which radon is measured.
• Certified measurement provider. Use an AARST/NRPP-certified measurement professional. Many sellers and buyers do not realize that a $20 mail-in kit, while useful for a homeowner spot check, is generally not the right instrument for a transaction. Continuous radon monitors (CRMs) are preferred — they record hourly readings and can detect tampering with closed-house conditions.
• Test location. The test is placed in the lowest livable level — finished basements, walk-out lower levels, or the lowest floor a buyer would occupy. Not in a furnace closet, not next to an exterior door, and not at the level of incidental disturbance.
• Most real-estate tests run 48 hours. Some agents request longer (up to 96 hours) for conditions or seasonal sensitivity.

For sellers

If you are listing your NH home — or even thinking about it in the next 12 months — there is a strong argument for testing for radon now, before the buyer's inspector does it for you. The reasons are practical:

1. You control the timeline. A radon result above 4.0 pCi/L mid-transaction creates pressure. Testing on your own schedule eliminates that pressure.
2. Mitigation as a marketing point beats mitigation as a concession. "Radon mitigation system installed in [year]" on the disclosure is a positive; a result in the high single digits during inspection is a negotiation.
3. Costs are predictable. A standard SSD mitigation system on a NH single-family home runs $1,000–$2,500 installed. Closing-table credits often exceed that — and credits do not solve the problem for the next buyer either.
4. Disclosure works in your favor. NH does not have the same statutory radon disclosure language as some neighboring states, but a clear, documented "tested at X, mitigated to Y" record materially improves the buyer's confidence.

If you are testing pre-listing and the result is below 2 pCi/L, you have documentation to share with the listing. Between 2 and 4, you can choose to mitigate proactively or document and disclose. At or above 4, plan to mitigate before listing or be prepared for the conversation later.

For buyers

If you are buying a home in NH, build a few days into your inspection contingency for radon testing — typically the test occurs on the same trip as the home inspection, with the device retrieved 48 hours later. Choose a certified measurement provider; ask the inspector who they use and verify NRPP credentials.

If your result comes back at or above 4.0 pCi/L, you have several paths:

• Ask the seller to install mitigation before closing, with you (the buyer) selecting or approving the installer.
• Ask for a closing credit equal to the cost of mitigation, and install yourself shortly after move-in.
• Walk away under the inspection contingency if other inspection findings combine to make the deal not work.

In our experience, option one tends to produce the best long-term outcome. The work gets done before move-in, the seller pays directly, and the buyer inherits a documented system with verification testing. That said, the right answer depends on your specific transaction.

On the in-between range — 2 to 4 pCi/L — the EPA recommends considering mitigation. Many NH buyers do mitigate at this level because the cost is modest and the lifetime risk math is favorable.

For realtors

Radon is a recurring transaction friction point that experienced NH agents learn to manage. A few tactical points that help:

• Have a vetted mitigation contractor in your back pocket. When a high result lands during inspection, the question "who can do this on our timeline?" needs an immediate answer. Mitigation work scheduled within 5–7 business days is normal for ARM and most quality NH contractors.
• Pre-empt the question with sellers. When you take a NH listing, raising radon during your initial walkthrough ("have you tested in the last two years?") usually leads to a better outcome for everyone. Pre-emptive testing reduces transaction risk.
• Know your standards. Saying "we use AARST-protocol testing with a continuous monitor" signals professionalism to buyers and to other agents. The MAH-2019 standard is the right reference.
• Mitigation appearance matters. Listing photos will include the mitigation system. A clean, well-routed exterior pipe with no daisy-chains and a quiet fan is a feature; a sloppy install is a deduction. This is a real differentiator among NH installers.
• Plan for radon-in-water on private wells. If the home is on a well, water radon should be tested in addition to indoor air. Water radon contributes to indoor air radon and may need its own treatment system. Builders, lenders, and buyers occasionally miss this; you should not.

How quickly can mitigation be installed?

Most single-family mitigation projects in NH install in a single day once scheduled. From a buyer's accepted offer with a high radon result, a realistic timeline is:

5. Day 1–2: Site assessment and quote (often same-day for transaction work).
6. Day 3–10: Installation (usually a 4–8 hour job for SSD).
7. Day 10–14: Post-mitigation test confirming the system has reduced radon below the action level.

Tighter timelines are achievable but should be communicated to the contractor as a transaction-timeline job from the first call.

Frequently asked questions

Does NH require radon testing in real estate transactions?

NH does not statutorily require testing, but most purchase agreements give the buyer the right to test inside the inspection contingency. In practice, radon testing is part of the great majority of NH transactions.

Who pays for the test?

Customarily, the buyer commissions and pays for the test as part of inspection costs. The amount is small — typically $150–$250 for a continuous-monitor test.

Who pays for mitigation?

Negotiable. Most NH transactions resolve a high radon result either with the seller paying for mitigation directly or with a credit to the buyer at closing.

How long does a mitigation system last?

Components are durable. Vent pipe and structural elements last indefinitely. The fan typically runs 8–10 years before replacement. The system overall is treated as a permanent part of the home.

Do I need to disclose a previously installed mitigation system to future buyers?

Yes, and you should — it is a positive disclosure, not a negative. A documented, professionally installed system is a value-preserving feature.

What if the result is just barely above 4 pCi/L?

Mitigation is still recommended. The action level is a single threshold, not a guarantee of safety below it. Systems that take a 4.5 pCi/L home down to under 1.0 pCi/L are common and the cost is the same.

Get a transaction-timeline quote

If you are a buyer, seller, or realtor in NH and need radon testing or mitigation on a real estate timeline, ARM can help. Call 603-644-1207 to schedule, or request a quote at radonh2o.com/contact. If you are a realtor and would like to be added to our priority-scheduling list for transaction work, mention that on first contact.