Radon Testing When Buying a Home: What You Need to Know

Always Test — Here's Why

Radon is invisible, odorless, and the second-leading cause of lung cancer in the US. It varies significantly from house to house — neighbors on the same street can have readings 10× apart based on foundation type, sub-slab material, and construction details. You cannot predict a home's radon level without testing.

In high-radon states (Colorado, Pennsylvania, Minnesota, Ohio, Illinois, Indiana, Iowa, Wisconsin, and others), testing is standard practice and skipping it is considered due diligence negligence by most real estate attorneys.

How Testing Works During a Purchase

Option 1: Include it in the inspection contingency

Add radon testing to your inspection contingency. Most home inspectors either perform radon testing themselves or can arrange it as an add-on. The test runs 48 hours (short-term charcoal canister), the home is closed up (windows shut, no HVAC changes) during the test period, and results come back within 3–5 days.

Cost: $100–$200 as an inspection add-on, or $25–$75 if you purchase and deploy your own test kit.

Option 2: Use a certified radon tester

In some states, you can hire a separate NRPP-certified measurement professional to conduct the test. This is the most rigorous approach — the tester is independent of both the seller and the inspector.

Option 3: Ask for seller's test records

Some sellers have existing test results. These are useful context but should not replace a current test — radon levels can change with renovations, HVAC changes, or changes in building pressure.

What the Results Mean

Below 2.0 pCi/L: Low risk. No action required, though you may want to retest every few years.

2.0–3.9 pCi/L: Below the EPA action level but above the WHO guideline. Many buyers proceed with no action; health-conscious buyers may negotiate a modest credit or plan to mitigate after closing.

4.0–7.9 pCi/L: Above the EPA action level. Standard negotiation territory. Mitigation typically costs $1,000–$2,000 for most slab homes — a reasonable seller credit or concession.

8.0–14.9 pCi/L: Significantly elevated. Mitigation is essential. Expect more aggressive negotiation — a $1,500–$2,500 credit, a price reduction, or seller-paid mitigation before closing.

15 pCi/L and above: Severely elevated. Some buyers walk; most renegotiate significantly. Mitigation at this level is effective but may require a professional assessment to ensure the right system design. A seller who mitigates at this level before listing will have a much smoother transaction.

Negotiating Radon in a Purchase

If the test comes back above 4.0 pCi/L, your options:

1. Ask the seller to mitigate before closing. This is cleanest — you close with a working system and a post-mitigation test confirming results. Downside: adds 1–2 weeks to the timeline.

1. Negotiate a credit. Get two or three mitigation quotes. Ask for a credit at the higher end of the range — if quotes come in at $1,200–$1,800, ask for a $2,000 credit to cover installation and a contingency buffer.

1. Price reduction. Less common but appropriate if the seller is unwilling to mitigate or credit.

1. Walk away. Radon is entirely fixable — it's rarely a reason to kill a deal — but if the seller is uncooperative and the home has other issues, it can be the final straw.

What not to do: Don't accept a seller's verbal assurance that "we've never had a problem" or "the house was just renovated." Neither statement has any bearing on radon levels. Only a test determines the level.

If the Home Already Has a Mitigation System

Many homes in high-radon states already have systems. Before closing:

1. Ask for documentation — installation date, pre- and post-mitigation test results, fan model
2. Inspect the system — check the manometer (the liquid-filled warning device on the pipe). Levels should be unequal, indicating negative pressure. If they're equal, the fan has failed.
3. Retest anyway — a short-term test after moving in gives you a current baseline. Fan age matters: systems over 10 years old may have diminished performance.

States With Real Estate Radon Disclosure Laws

Most states require sellers to disclose known radon issues or test results. A few require testing. Check your state's specific requirements — your real estate agent should know, but verify independently.

Regardless of disclosure law, testing is always your right as a buyer during the inspection period.

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