What is a safe radon level?

There is no completely safe radon level — any exposure carries some risk. The EPA action level is 4 pCi/L (picocuries per liter): at or above this level, the EPA recommends installing a mitigation system. The WHO recommends action at 2.7 pCi/L. The average indoor level in the US is 1.3 pCi/L. The average outdoor level is 0.4 pCi/L. A well-installed mitigation system typically reduces levels to below 2 pCi/L (often below 1 pCi/L). If your level is between 2 and 4 pCi/L: the EPA says to consider mitigation (the risk is still meaningful). Below 2 pCi/L: generally considered acceptable. Re-test every 2 years regardless of the result.

How much does radon mitigation cost?

Sub-slab depressurization (most common): $800-$2,500 installed. Crawl space sub-membrane depressurization: $1,000-$3,000. Annual electricity for the fan: $50-$100. The system runs 24/7 and typically lasts 15-25 years before the fan needs replacement ($150-$300 for the fan). Post-mitigation testing: $10-$30 (DIY kit) or $100-$300 (professional). Some states offer radon mitigation tax credits or assistance programs. The cost of mitigation is a fraction of the health risk: the EPA estimates the lifetime lung cancer risk from living in a home at 4 pCi/L is about 7 in 1,000 for non-smokers and 62 in 1,000 for smokers.

Can I test for radon myself?

Yes. DIY radon test kits are widely available at hardware stores and online for $10-$30. Instructions: place the test device in the lowest livable area of your home (usually the basement). Keep windows and exterior doors closed for 12 hours before the test and during the entire test period (2-7 days for short-term tests). After the test period: seal the device and mail it to the lab (postage is usually pre-paid). Results come back in 1-2 weeks. For a more accurate reading: use a long-term test (90 days to 1 year). For real estate transactions: most lenders and buyers require a professional test with tamper-proof continuous radon monitors.

Does every home have radon?

Every home has some level of radon — the question is how much. Radon comes from the natural decay of uranium in the soil beneath your home. The level depends on the uranium content of the local soil and rock, the permeability of the soil, the construction of the home (slab, basement, crawl space), and the air pressure dynamics of the home. The EPA estimates that 1 in 15 US homes has radon levels at or above 4 pCi/L. Radon levels vary house to house — your neighbor's level tells you nothing about yours. The only way to know is to test. Every home should be tested regardless of location, age, or construction type.

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Home Improvement

Radon Testing Guide: How to Test & Mitigate Radon in Your Home

Lumberama Editorial Team, Home Safety & Environmental Specialists Aug 4, 2026 13 min read

What Is Radon

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It is colorless, odorless, and tasteless — you cannot detect it without testing. Radon seeps into homes through cracks in the foundation, gaps around pipes, construction joints, and any opening where the house contacts the soil. It is the second leading cause of lung cancer in the United States (after smoking), responsible for approximately 21,000 lung cancer deaths per year (EPA estimate). The EPA recommends action when radon levels are at or above 4 picocuries per liter (pCi/L). The average indoor radon level in the US is 1.3 pCi/L. The average outdoor level is 0.4 pCi/L. There is no safe level of radon exposure — any exposure carries some risk — but the EPA action level of 4 pCi/L balances risk reduction with practical achievability.

How to Test

Short-term tests (2-7 days): Charcoal canister or alpha-track detector placed in the lowest livable area of the home (typically the basement). Closed-house conditions: keep windows and exterior doors closed for 12 hours before the test and during the entire test period (except for normal entry/exit). Cost: $10-$30 for a DIY kit (available at hardware stores and online). You place the device, leave it for the specified period, seal it, and mail it to a lab. Results in 1-2 weeks.

Long-term tests (90 days to 1 year): Alpha-track detector or electret ion chamber. More accurate because radon levels fluctuate daily and seasonally. Provides a better annual average. Cost: $20-$50.

Professional testing: A certified radon tester places continuous radon monitors (CRMs) that take readings every hour for 48+ hours. Tamper-proof and produces detailed data. Cost: $100-$300. Required or recommended during real estate transactions in many states.

Continuous radon monitors (homeowner): Electronic devices (Airthings, Radon Eye, Safety Siren) that continuously measure radon. Provide real-time readings and long-term averages. Cost: $100-$250. Good for ongoing monitoring after mitigation.

Mitigation Systems

Sub-slab depressurization (SSD): The most common and effective method (reduces radon by 90-99%). A pipe is inserted through the basement floor into the gravel or soil beneath the slab. A fan (mounted in the attic or on the exterior of the house) draws radon-laden air from beneath the slab and vents it above the roofline, where it disperses harmlessly. The system runs continuously (the fan uses about as much electricity as a 75-watt light bulb). Cost: $800-$2,500 (installed).

Sub-membrane depressurization: For homes with crawl spaces (dirt floors). A heavy-duty plastic sheet (membrane) is sealed over the dirt floor and up the walls. A pipe and fan draw radon from beneath the membrane and vent it outside. Cost: $1,000-$3,000.

Sealing cracks and openings: Sealing cracks in the foundation, gaps around pipes, and sump pit covers reduces radon entry points. Not effective as a standalone solution (radon finds other paths). Used in conjunction with active depressurization.

Heat recovery ventilator (HRV) or energy recovery ventilator (ERV): Increases ventilation to dilute radon. Less effective than active soil depressurization but can be used when SSD is not feasible. Also improves overall indoor air quality.

When to Test

Every home should be tested for radon — regardless of location, age, or construction type. Radon levels vary house to house (one home can be high while the neighbor is low). Test: when buying a home (standard in most real estate transactions), when selling a home (many buyers will request it), after any major renovation that changes the foundation or ground contact (finishing a basement, adding a sump pit, foundation repair), every 2 years (EPA recommendation) or after any structural changes to the lowest level, and if you have never tested. High-risk zones: the EPA has mapped radon zones for the US. Zone 1 (highest potential) covers much of the northern US, the Appalachian region, and parts of the Midwest and Rocky Mountain states. But elevated radon has been found in every state — testing is the only way to know.