Radon Test Came Back High? Your 30-Day Action Plan

The EPA action level for radon is 4 pCi/L. If your test came back at or above that number, you have a real problem to solve, but you don’t have an emergency on your hands. Most “high” readings sit between 4 and 10 pCi/L, and the right response is a deliberate one taking about four weeks: confirm the reading, find a qualified contractor, install a system, and verify the result.

This is the plan.

First, Understand What Your Result Means

The 4 pCi/L threshold is the EPA’s “action level,” not a danger line. It’s the point at which the agency recommends taking corrective action, set conservatively because radon exposure compounds over decades. A reading of 4.2 pCi/L is not meaningfully more dangerous than 3.8 pCi/L on any given day. What matters is the long-term average.

A few things to keep in mind as you read your result:

• Short-term tests (2 to 7 days) tend to overstate true exposure. Radon levels swing day to day with weather, ground moisture, and how often you open windows. A two-day reading that lands at 6.5 pCi/L often averages closer to 4 over a full year. This is why long-term tests matter for confirmation.
• The 2 to 10 pCi/L range is by far the most common “high” result. If your number is in this band, you’re in well-understood territory. Mitigation contractors solve this kind of problem every week.
• Above 10 pCi/L compresses the timeline but doesn’t change the destination. Higher readings shift you toward faster action, not panic. A reading of 20 pCi/L is roughly equivalent to a smoking habit over a lifetime of exposure, which is serious, but not “leave the house tonight” serious.

The right mindset is the same one you’d use after a moderately bad blood test result. Confirm the finding, line up the right specialist, and follow the protocol.

Days 1 to 7: Confirm the Reading

Before you spend $1,500 on mitigation, make sure the number is real.

Option A: Long-term test. Order a 90-day or 12-month alpha-track detector. These cost $20 to $40 and give you a true average across changing weather and household routines. This is the most accurate confirmation you can do.

Option B: Second short-term test. If you’re under time pressure — typically because of a real estate transaction — run a second short-term test in parallel with arranging contractor quotes. Place this one in a different lowest-level living area than the first test. See our radon testing guide for placement specifics.

A few rules for the confirmation test:

• Place the detector in the lowest occupied level of the home, in a room where someone spends meaningful time. Not in a closet, not in a crawl space, not next to an exterior wall, not on the floor.
• Run the test under closed-house conditions: doors and windows kept closed except for normal entry and exit. For short-term tests, this rule applies for the 12 hours before the test starts and the full duration of the test.
• Don’t touch your HVAC settings during the confirmation period. Don’t open windows to “air out” radon — you’ll just contaminate the test, not the problem.

Our guide on DIY vs professional radon testing covers which kits actually meet AARST measurement standards.

Days 7 to 14: Interview Contractors

While the confirmation test is running, start lining up contractors. The single most important screening criterion is certification. Look for NRPP (National Radon Proficiency Program) or NRSB (National Radon Safety Board) credentials, and verify them on the issuing organization’s database, not on the contractor’s website. Both bodies maintain searchable directories of currently active certified mitigators.

When you talk to candidates, four questions separate the good ones from the rest:

1. “Will you do a diagnostic visit before quoting?” A good contractor walks the home, checks foundation type, looks for entry points, and discusses where the suction will be most effective. A contractor who quotes off a phone call alone is guessing.
2. “Is post-mitigation testing included in the quote?” It should be. AARST standards call for it, and a contractor who skips this step is signaling they don’t want to be measured.
3. “What’s the warranty on the fan, and what are the conditions?” Fans typically last 5 to 10 years. Lifetime warranties without conditions are a red flag, not a feature. A serious contractor will warranty the install for 1 to 5 years and the fan separately to the manufacturer’s terms.
4. “What guaranteed result will you commit to in writing?” A reputable contractor will guarantee the system reduces your levels to under 4 pCi/L. Many will guarantee under 2 pCi/L.

Expect 2 to 3 quotes. Expect them to vary by $500 to $1,500 for the same scope of work. The reasons for variance are real (crew availability, fan model, post-install scope), not arbitrary, but the cheapest quote is rarely the right answer. Our guide on choosing a radon contractor lays out the full vetting process.

Days 14 to 21: Choose a System and Schedule Install

Once you have your confirmed reading and your shortlist of contractors, system selection comes next. For most homes the answer is simple: active sub-slab depressurization (ASD).

Active sub-slab depressurization drills one or more suction points through the basement or slab foundation, runs PVC vent piping up through the home (typically inside a closet or chase) and out through the roof, and installs a radon-rated inline fan that creates negative pressure beneath the slab. The fan pulls radon gas before it ever enters the home. This is the workhorse system, and it solves the problem for the large majority of houses.

Sub-membrane depressurization is the crawl-space variant. If your home has a crawl space (full or partial), the contractor lays a heavy polyethylene vapor barrier across the crawl floor, seals it to the walls, and pulls suction from beneath that membrane. The mechanics are the same, but the membrane needs to be intact and properly sealed — see our crawl space repair directory if your contractor flags moisture or grading issues that need fixing first.

Two technical details to ask about during the install scheduling:

• Diagnostic vacuum test. Before drilling, your contractor should perform a Pressure Field Extension test. This involves drilling a small hole, applying suction, and measuring how far the pressure field extends beneath the slab. The result determines where suction points go and how many you need. Skipping this step is a sign the install will be guesswork.
• Permits and HOAs. Most municipalities don’t require a permit for radon mitigation, but a handful do (mostly for the electrical work and roof penetration). HOAs occasionally object to exterior vent stacks. Confirm both before scheduling.

For most homes, install is a one-day job. Pricing varies by foundation and complexity — see our cost breakdown for what to expect.

Days 21 to 30: Install, Test, Verify

The install itself is straightforward. Expect a crew of two for most of a workday: drilling, piping, fan placement, sealing, and clean-up. You don’t need to leave the house, but expect noise and dust in the basement.

Once the system is energized, wait 24 to 48 hours for it to stabilize before testing. The negative pressure field needs time to develop and the air in the home needs time to clear.

The post-mitigation test should be performed by the contractor (most include it; if yours doesn’t, run one yourself). Realistic success looks like this:

• Under 2 pCi/L is the target most reputable contractors will guarantee.
• Under 4 pCi/L is the EPA floor and the minimum acceptable result.
• No measurable change means something is wrong — usually a missed entry point or insufficient suction. A good contractor will diagnose and fix it under the original quote.

Once the post-test confirms the system is working, your job shifts to maintenance. Retest every 2 years, replace the fan when it dies (every 5 to 10 years), and keep an eye on the system’s pressure gauge (the U-tube manometer mounted on the vent pipe). Our radon mitigation maintenance guide covers the year-by-year routine.

What If Your Reading Is Above 10 pCi/L?

Compress the timeline.

You can skip the long-term confirmation test and move directly to contractor interviews. The reading is high enough that a second short-term test for confirmation (placed differently than the first) is sufficient, and you should run that test in parallel with quotes, not before them.

If you have young children or anyone with a respiratory condition, two practical adjustments while you wait for mitigation:

• Avoid using the lowest level of the home as a primary occupied space. Move bedrooms upstairs if feasible. This is not a “must” — radon exposure is a long-term cumulative risk, not an acute one — but it reduces exposure during the few weeks before mitigation.
• Open windows when weather permits. This isn’t a fix, but it does temporarily reduce indoor levels. Don’t run heavy ventilation continuously (it creates other problems), but normal airing-out during mild weather is fine.

There is no medical “you’ve been exposed, now what” treatment for radon, because the risk model is cumulative over decades. The right response is to reduce future exposure, which is exactly what mitigation does. If you have specific health concerns, your primary care doctor can refer you to a pulmonologist, but in most cases the answer is “install the system and stop worrying about it.”

For context on what readings in this range mean, see our guide on what radon level is dangerous.

What If You’re in the Middle of a Home Purchase?

Real estate timing changes the calculus.

The buyer typically pays for the test (it’s part of inspection), and the result enters the negotiation. In most markets, sellers either install mitigation before closing or credit the buyer at closing for the work. The typical credit is $1,500 to $2,500, which approximates the going install rate plus a small premium for the inconvenience.

A few things to know:

• The EPA’s “Radon Resistant New Construction” features in newer homes are not a guarantee. They’re a passive system that may or may not need a fan added. If you’re buying a newer home with an RRNC system, run a test — don’t assume the system is already doing the work. See our companion guide on RRNC in new construction for what the rough-in does and doesn’t include.
• A real estate radon test should be a tamper-resistant continuous monitor, not a passive kit. Most home inspectors who run radon tests use these. The data record from a continuous monitor protects both sides from disputes about whether windows were left open.
• Don’t let the deal die over the test. Mitigation is solvable. The cost is small relative to a closing price. Push for the seller credit, do the install in the first 30 days post-closing, and move on.

Our radon and real estate guide covers the negotiation details and timing specifics.

Frequently Asked Questions

Should I leave my house if radon is high? No. Radon is a long-term exposure risk, not an acute one. Even readings of 20 pCi/L don’t justify evacuation. The right response is to install mitigation within a reasonable window (30 to 60 days for moderately high readings, faster for readings above 10 pCi/L).

Can I open windows to lower radon? Temporarily, yes. Sustained ventilation isn’t a fix — you’ll fight the HVAC system, lose heat or cooling, and the levels will rebound when windows close. Mitigation is the only durable solution.

How fast does mitigation actually work? The fan creates the negative pressure field within minutes of being energized. Levels in the home drop substantially within 24 hours. The 24 to 48 hour wait before post-testing is to let levels stabilize at their new baseline, not because the system needs that long to start working.

Will a high radon reading affect my home’s value? Unaddressed, yes. Mitigated, no — and in many high-radon markets a documented mitigation system is a selling point, not a liability.

Do I need to retest every year after mitigation? Every 2 years is the AARST recommendation. The fan can fail silently, and the only way to catch it is to retest. Visual inspection of the pressure gauge between tests catches most fan failures earlier.

Find an NRPP-certified radon mitigation contractor in your area and start the 30-day plan today. Most homes are fully mitigated within four to six weeks of the first high reading.