What to do after a high radon test result

A high radon test result means the air in the tested room held more radon than EPA’s action level of 4 picocuries per liter, or landed in the 2–4 band where EPA says consider fixing. It does not mean the house is unsafe to enter today. The next steps are orderly: check that the test was valid, confirm the number, and then spend money in proportion to what the number actually says.

Read the number before you react

Radon risk is cumulative. It comes from years of breathing elevated concentrations, not from one week of them, which is why a reading of 6 pCi/L is a reason to act within weeks rather than to move out tonight. EPA estimates about 1 in 15 US homes sits at or above the action level, so the result is common rather than exotic.

The number also needs context. A short-term kit measures 2–4 days. A long-term kit at $20–$50 measures 90 days or more, and its average is the better basis for a decision near the line. A continuous monitor at $100–$200 shows how the level moves hour by hour, which is useful for understanding the house but not for a real-estate decision.

Where the kit sat matters as much as what it read. A result from a basement family room describes a room people use every evening. The same result from a sealed crawl space describes a space nobody occupies, and calls for less urgency. The lowest lived-in level is the one that governs exposure, which is why the kit belongs there and not wherever the shelf was free.

Confirm the result

Before any contractor visits, check two things: whether the test conditions were valid, and whether the number reproduces. The first is a matter of record. EPA’s closed-house rule is 12 hours before and during the exposure, with windows and exterior doors shut, so a test taken with a slider open is a reason to retest rather than to mitigate.

The second is cheap. A second short-term kit costs $15–$45, and a certified measurement runs $150–$250. If the first reading was 12 pCi/L, the confirmation will not change the plan. If it was 4.4 pCi/L in a drafty week, the confirmation may save the entire project.

If the reading is between 2 and 4 pCi/L

EPA’s guidance in this band is to consider fixing, which is deliberately a judgment rather than an instruction. Three inputs make the decision easier: a long-term average, the lowest lived-in level, and whether anyone sleeps or works there.

A long-term kit gives the year-round number and removes the seasonal question, since a sealed January house and an open June house are not measuring the same thing. Sealing obvious openings — an airtight sump lid, caulk at slab cracks, gaskets on floor drains — is cheap, reversible and useful in either case. If the average sits near 4 and the house has a basement that gets used, a system is usually the reasonable call.

If the reading is 4 pCi/L or above

At or above the action level, EPA’s advice is to fix the home. That means a fan-based depressurization system, priced at $800–$2,500 installed with a national average near $1,200. The cost guide explains what moves the number, and the cost section covers the bands by system type.

Do not sign the first quote. The spread between bids in the same market is wider than the EPA band suggests, and the differences are usually visible in the line items: the fan model, the suction-point count, whether the permit is included, and whether the post-install test is included.

There is also no reason to air the house out while you wait. Opening windows lowers a reading, but the number that matters is the one the house produces when it is closed, which is how it spends the winter. A contractor who tests a ventilated house is measuring your open windows rather than your foundation.

Get three bids and compare the lines

Three quotes give you the local range and a sense of which contractor is explaining the house rather than selling a package. The foundation-type guide tells you what your foundation should require, which is the benchmark for judging whether a bid is describing your house.

A bid that names a “standard fan” and one suction point for a house with a crawl space and a basement is not a bid yet. It is an estimate of what the contractor hopes to find.

Sealing is not mitigation

Caulking cracks and fitting a sump lid reduces entry, and it is worth doing. It does not put the soil under negative pressure, and in a house reading well above the action level it will not bring the number under 2 pCi/L on its own.

The distinction matters because sealing is the cheapest-looking option on the list, and a homeowner with a 9 pCi/L result can spend a weekend on it and still need the system. Do the sealing as part of the project, not as a substitute for it.

The post-install test

The system is not finished when the fan starts. EPA calls for a test after the system has operated for at least 24 hours, with the house closed as it was for the original test. Below 2 pCi/L is the usual target, and a contractor who guarantees a level should put it in writing with a remedy if the test misses.

If the retest stays at or above 4 pCi/L, the answer is diagnosis, not a second system. The usual causes are an unsealed opening, a short-circuited suction field, a fan that is too small for the field, or a blocked pipe. All of them are cheaper to fix than a new install, and all of them are the installer’s responsibility under a competent guarantee.

Retest every two years

Radon levels move with the house: a new furnace, a finished basement, a changed exhaust fan or a renovated crawl space can all shift the pressure balance. EPA’s schedule is a retest every two years, and after any major renovation or HVAC change.

Keep the results together with the system label and the install paperwork. The testing section covers the conditions for a valid retest, and the comparison section explains what the alternatives to a full system actually do. A high reading is a fact about the house, not a verdict on it, and the sequence above turns it into a decision you can defend.