Radon Testing: What Every Home Buyer Needs to Know
Radon is invisible, odorless, and deadly — and it's present in homes across all 50 states. A $100–$200 test could be the most important thing you do before buying a home.
What Is Radon?
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil, rock, and water. It has no color, no odor, and no taste — making it completely undetectable without a test. It seeps up through the ground and can accumulate to dangerous concentrations inside homes.
Radon is present everywhere on Earth at low levels. The problem arises when it becomes trapped inside a building. When you breathe radon, the radioactive particles it emits damage lung tissue over time.
Radon is the #2 cause of lung cancer in the US, behind only cigarette smoking. The EPA and Surgeon General urge all Americans to test their homes. Unlike smoking, radon exposure is largely preventable.
The EPA Action Level: 4 pCi/L
Radon is measured in picocuries per liter (pCi/L). The EPA recommends taking action to reduce radon when levels reach 4 pCi/L or higher. Understanding where that number sits in context helps:
The baseline. Unavoidable background level from natural soil outgassing.
Typical indoor level. Still slightly above outdoor air, but generally considered acceptable.
EPA suggests considering mitigation in this range, especially for long-term occupants.
At this level, the EPA recommends mitigation. Risk is comparable to having 8 chest X-rays per day.
Significantly elevated risk. Equivalent radon-related lung cancer risk to smoking half a pack of cigarettes per day.
Rare but documented. Immediate mitigation required. Some homes in high-radon zones can reach 100+ pCi/L untreated.
Types of Radon Tests
There are three main approaches to radon testing. For a home purchase, the short-term test is standard — but understanding the differences helps you make the right call.
Most common for home purchases. Sent to a lab after collection. Results within 24–48 hours of lab receipt.
Captures seasonal variation. Best for understanding your true average exposure over time. Not practical for real estate transactions.
Provides hour-by-hour readings and tamper detection. Preferred by many inspectors for real estate testing. Results are immediate.
How Home Inspectors Perform Radon Testing
Most home inspectors offer radon testing as an add-on service. Here's what to expect:
All windows and exterior doors must remain closed for at least 12 hours before the test begins and for the entire test duration. Normal HVAC operation is fine. This prevents outdoor air from diluting the sample.
The detector is placed in the lowest livable area of the home — typically a finished basement or first floor if no basement exists. This is where radon concentration is highest. It's placed away from drafts, exterior walls, sumps, and high-humidity areas.
Short-term charcoal canisters remain in place for 48–96 hours (2–4 days is most common for real estate purposes, though up to 7 days is allowed). Continuous monitors provide readings throughout.
The canister is sealed and mailed to an accredited laboratory. Results are returned within 24–72 hours. Continuous monitors display results immediately at pickup.
Radon testing through a home inspector typically costs $100–$200 when added to a standard home inspection. Ordering it as a standalone service can cost more. Many inspectors bundle radon with mold or other specialty tests at a discount.
Highest Radon Risk States
While radon is present in all 50 states, geology significantly affects concentration levels. The EPA has mapped the US into three zones — Zone 1 states have the highest predicted average indoor radon levels (above 4 pCi/L). Testing is critical everywhere, but especially in these states:
Source: EPA Map of Radon Zones. Note: High radon levels have been found in all states — including Zone 2 and Zone 3 states. Never skip testing based on geography alone. A neighboring home can test at 1 pCi/L while yours reads 12 pCi/L.
Radon Mitigation: How to Fix High Levels
High radon is not a reason to walk away from a home. Mitigation is well-understood, widely available, and highly effective — typically reducing levels by 90% or more. Here are the main approaches:
The most common and effective method. A pipe is installed through the slab floor and a fan draws radon from beneath the foundation and vents it outside. Works on most home types.
Caulking and sealing cracks in foundation floors and walls reduces entry points. Often done in combination with ASD for maximum effect. Rarely sufficient as a standalone fix.
Increases fresh air circulation throughout the home, diluting radon concentration. Most effective in very tight, energy-efficient homes. Also improves overall indoor air quality.
In almost all cases, no. High radon is a solvable problem. A sub-slab depressurization system installed by a certified contractor will reliably bring levels below 2 pCi/L in the vast majority of homes — often below 1 pCi/L.
Use the test results as negotiating leverage: request that the seller install a mitigation system before closing, or negotiate a price reduction to cover the cost ($800–$2,500). Most sellers will cooperate — it's a well-understood issue with a clear, cost-effective solution.
Frequently Asked Questions
Yes — absolutely. Radon testing typically costs $100–$200 as an add-on to a home inspection. Radon is the #2 cause of lung cancer in the US, responsible for approximately 21,000 deaths per year. Testing is inexpensive, fast, and gives you critical health and safety information before you close on a home.
The EPA recommends taking action when radon levels reach 4 pCi/L (picocuries per liter) or higher. The average US home measures 1.3 pCi/L; outdoor air averages 0.4 pCi/L. Even levels between 2–4 pCi/L carry some risk, and the EPA suggests considering mitigation in that range as well.
Short-term tests take 2–7 days using a charcoal canister. Long-term tests run 90 days or more using an alpha track detector and give a more accurate year-round picture. Continuous electronic monitors provide real-time results. For home purchases, a short-term test is most common and fits within standard inspection timelines.
Yes. DIY radon test kits are available at hardware stores for $15–$30 and are EPA-approved. However, for a home purchase, having a certified inspector perform the test ensures proper placement, closed-house conditions are maintained, and results carry more weight in negotiations. Professional tests also include documentation useful for real estate transactions.