How to Test Home Radon Before Closing Day

Radon is easy to overlook because you cannot see it, smell it, or identify it during a walkthrough. Yet how to test home radon is one of the most practical questions to ask before purchasing a property, particularly when the inspection period is short and major decisions are still on the table. A properly conducted test gives buyers, sellers, and agents useful information about a health-related condition that can often be corrected.

Radon is a naturally occurring radioactive gas released as uranium breaks down in soil and rock. It can enter through cracks in slabs, sump pits, pipe openings, crawlspaces, and other gaps between a home and the ground. Any home can have elevated radon, regardless of age, construction type, or whether a neighbor’s result was low. Testing the specific property is the only way to know what is happening there.

How to Test Home Radon During a Real Estate Transaction

For a purchase or sale, the most reliable approach is a short-term radon test performed by a qualified professional using an approved device and standard testing procedures. Short-term tests typically run for at least 48 hours, making them well suited to an inspection contingency or closing timeline.

A professional may use a continuous radon monitor, which records hourly readings and can help identify whether the test conditions were disturbed. Other approved short-term methods may use charcoal-based collection devices. The right option depends on the property, the schedule, and the reporting requirements for the transaction.

At Miller Home Inspection, radon testing is treated as a clear part of due diligence, not an alarm tactic. The goal is to document the result, explain what it means, and give clients information they can use in a repair discussion or purchase decision.

Place the test in the right area

The device should be placed in the lowest level of the home that could be regularly occupied. In a house with a basement that could serve as living space, that is usually the basement. If the lowest level is an unfinished crawlspace that cannot be occupied, the test is commonly placed on the first livable floor instead.

Placement within the room matters too. The device should be kept away from exterior doors, windows, high heat, direct sunlight, excessive humidity, and moving air from vents or fans. It should not be placed in a kitchen, bathroom, laundry room, or closet. Those details may sound small, but they help produce a result that reflects normal indoor radon conditions rather than a distorted reading.

Keep closed-house conditions during the test

Short-term testing depends on closed-house conditions. Exterior windows and doors should remain closed as much as practical for at least 12 hours before the test starts and throughout the testing period. Normal entry and exit is fine, but leaving a window open overnight or airing out the house can affect the result.

Heating and air conditioning systems can run normally. Whole-house fans, window fans, and other equipment that brings in outside air should generally not be used. A qualified tester will explain the requirements before placement and document test conditions when the device is retrieved.

This is one reason a casual DIY test can be difficult during a transaction. An overzealous seller trying to help, a contractor opening windows, or a vacant-home thermostat issue can compromise the testing conditions. A continuous monitor may flag unusual patterns, allowing the parties to address an invalid test rather than relying on questionable data.

Understanding a Radon Test Result

Radon results are generally reported in picocuries per liter of air, written as pCi/L. The U.S. Environmental Protection Agency recommends taking action when a home’s radon level is 4.0 pCi/L or higher. It also advises considering mitigation for levels between 2.0 and 4.0 pCi/L, because there is no known safe level of radon exposure.

A result below 4.0 pCi/L is not a guarantee that radon will never be present at a higher level. Radon can fluctuate with weather, soil moisture, seasons, heating patterns, and how the house is used. Still, a properly completed short-term real estate test is valuable evidence for the decision at hand.

If a result is 4.0 pCi/L or higher, do not assume the deal has to stop. Radon mitigation is a well-established process. In many homes, a mitigation contractor installs a system that draws radon gas from beneath the foundation and vents it safely above the roofline. The exact design depends on whether the home has a slab, basement, crawlspace, or a combination of foundation types.

The next conversation should be practical: Who will arrange the mitigation work? Will it be completed before closing or addressed through a credit? Will the system be retested after installation? A post-mitigation test is essential because the system should be verified, not simply assumed to work.

Short-Term vs. Long-Term Radon Testing

A short-term test is usually the right choice when a buyer needs an answer within days. It fits the pace of a home inspection and provides a documented result while negotiations are active. Its trade-off is that it captures a limited window of conditions.

A long-term test runs for more than 90 days and gives a better picture of a home’s average radon level over time. It is often a smart choice for homeowners who are not facing a transaction deadline, especially if a short-term result falls near an action threshold or if they want additional reassurance after moving in.

These options are not competitors. Short-term testing answers the immediate real estate question. Long-term testing can add confidence later, when the household has settled into normal routines. If the initial result is high, however, waiting months for a long-term average is usually not the preferred response. Address the elevated result with a qualified mitigation professional and verify the outcome.

Should You Use a DIY Radon Kit?

A DIY kit can be a reasonable way for an existing homeowner to screen for radon, particularly when there is no closing deadline. Follow the instructions exactly, use the required closed-house conditions, and send the device to the lab promptly. A low-cost kit is better than no test at all.

For a real estate transaction, however, professional testing has real advantages. It provides clearer documentation, controlled placement, a defined test start and end time, and a report that buyers, sellers, agents, and lenders can review. If the result may support a repair request, a professional process reduces uncertainty for everyone involved.

Be cautious about trying to improve the result by opening windows, sealing visible cracks right before testing, or running unusual ventilation equipment. Those actions do not solve the underlying condition, and they can make the test less representative. If a property needs mitigation, finding that out early is far more useful than creating a temporary lower reading.

When Sellers Should Test for Radon

Sellers can choose to test before listing, especially if they want fewer surprises during negotiations. If the level is elevated, they have time to obtain mitigation estimates, complete the work, and retain the post-installation test result. That can make the property easier to present with confidence.

There is a trade-off. A pre-listing test does not always eliminate the buyer’s desire for an independent test, and radon levels can vary. Still, a documented mitigation system and successful follow-up result are often meaningful information for prospective buyers.

For buyers, adding radon testing to the inspection period is a measured way to protect yourself. It is not a judgment on the home or the seller. It is a straightforward check of a condition that cannot be evaluated by sight alone. Ask for the test to be scheduled early enough that there is time to receive the report, discuss the result, and make a clear decision before your contingency deadline arrives.