What Is Radon and Why Should You Care?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It seeps into homes through cracks in foundations, gaps around pipes, construction joints, and even through well water. You cannot see, smell, or taste it. The only way to know your radon level is to test.
The EPA has set the action level at 4 picocuries per liter (pCi/L). At or above this level, the EPA recommends mitigation. However, there is no truly safe level of radon — even below 4 pCi/L, some risk exists. The EPA recommends considering mitigation at levels between 2 and 4 pCi/L. The average indoor radon level is 1.3 pCi/L; the average outdoor level is 0.4 pCi/L.
1. How to Test for Radon
Short-term tests (2-7 days): Charcoal canister or continuous radon monitor placed in the lowest livable level of the home. DIY kits cost $15-$30 at hardware stores (includes lab analysis). Results in 1-2 weeks after sending the kit to the lab. Professional short-term testing: $100-$200.
Long-term tests (90+ days): Alpha track detectors or electret ion chambers measure the average over 3-12 months. More accurate than short-term tests because radon levels fluctuate daily and seasonally. Cost: $20-$40 for DIY kits.
Continuous radon monitors: Electronic devices that measure radon in real-time. Consumer models ($100-$250) like Airthings and RadonEye provide ongoing monitoring with phone alerts if levels spike. Professional monitors are used during real estate transactions.
2. Radon Mitigation Systems
If testing shows levels at or above 4 pCi/L, mitigation is recommended. The most common method is sub-slab depressurization (SSD): a pipe drilled through the foundation slab connects to a fan that draws radon from beneath the house and vents it above the roofline. This method reduces radon levels by up to 99%.
Cost: $800-$1,500 for most homes. Installation takes one day. The fan runs continuously and costs $50-$100 per year in electricity. The system is virtually maintenance-free — just check that the fan is running (a manometer gauge on the pipe shows system pressure) and replace the fan every 5-10 years ($150-$300).
3. Radon Entry Points
Radon enters through any opening in contact with the soil: cracks in the slab, gaps around utility penetrations (pipes, wires), construction joints where walls meet the floor, sump pump openings, and basement floor drains. Sealing these openings alone does not solve radon problems — you need active ventilation (mitigation system) — but sealing supports the mitigation system's effectiveness.
4. High-Risk Areas
Radon risk varies by geography — areas with high uranium content in soil and rock have higher levels. The EPA has mapped radon zones across the country. Zone 1 (highest risk) areas have a predicted average above 4 pCi/L. However, elevated levels have been found in every state, and neighboring houses can have dramatically different levels. The only way to know your home's level is to test.
Radon in Real Estate Transactions
Radon testing is a standard part of the home inspection process in most markets. If elevated levels are found, the buyer typically requests that the seller install a mitigation system before closing — a reasonable request since mitigation costs $800-$1,500 and is straightforward. Some sellers proactively test and install mitigation before listing to remove the concern entirely.
Homes with existing, properly functioning mitigation systems are not stigmatized — the system shows the issue was identified and resolved. Post-mitigation radon testing confirming safe levels provides buyer confidence.
If you are buying, always test for radon, regardless of geographic zone. If you are selling in a high-radon area, consider pre-listing testing and mitigation. Your real estate agent can advise on local radon expectations and negotiation norms.