When and Why to Schedule a Radon Retest for Your Home

If you tested your home for radon a few years ago and the results came back below the action level of 4 pCi/L, you might assume the problem is solved for good. But radon levels in a house can change. Shifts in the soil, changes to your heating system, or even a major renovation can alter how radon enters the building. That is why a radon retest is not just a box to check off when selling a home. It is a sensible part of long-term indoor air quality management, especially in areas like Metro East Illinois where the geology can produce pockets of elevated radon.

I have seen homes in Belleville and Edwardsville test low one year and then show readings above the U.S. EPA radon guide the next. The reasons vary, but the pattern is common enough that I recommend homeowners consider retesting every two to three years, or sooner if something changes in the house. The first test gives you a snapshot. A radon retest gives you a more reliable picture over time.

Why Radon Levels Fluctuate

Radon comes from the natural decay of uranium in soil and rock. It moves up through the ground and enters buildings through cracks in the foundation, gaps around pipes, and other openings. The rate of entry depends on factors like soil moisture, barometric pressure, and how tightly the house is sealed. A wet spring can push more radon into a basement than a dry fall. A new furnace that changes the air pressure inside the house can also affect the readings.

For homeowners in O'Fallon IL and Collinsville, seasonal differences matter. Short-term radon test results taken in the winter, when windows are closed and the house is under negative pressure, can be two or three times higher than a test done in the summer with windows open. That is why a single test, while useful, is not definitive. A radon retest conducted in a different season or after a home improvement can catch a problem that the first test missed.

When a Retest Makes the Most Sense

There are several situations where I strongly advise a retest. The first is after any major structural work. If you have added a room, finished a basement, or replaced your foundation drainage system, the pathways for radon may have changed. A radon-resistant new construction home is built with a barrier and sometimes a passive vent stack, but even those systems can degrade or become blocked.

The second situation is after a mitigation system has been installed. If you hired a company like Air Sense Environmental to install a radon fan system or a sub-slab depressurization system, the follow-up test is critical. The U.S. EPA radon guide recommends testing within thirty days of activation to verify that the system is bringing levels below the action level of 4 pCi/L. I have seen cases where a fan was undersized or a suction point was placed in the wrong spot, and the retest caught it before the homeowner assumed the problem was fixed.

A third reason is simply time. Soil settles. Cracks widen. A house that tested at 2 pCi/L five years ago might now be at 6 pCi/L. Without a radon retest, you have no way of knowing. The only way to be sure is to test again.

Choosing the Right Testing Method for a Retest

When you go back for a retest, you have options. The type of radon detector you choose depends on how much time you have and what kind of information you want.

A short-term radon test, typically using a charcoal canister or an E-PERM electret, stays in the house for two to seven days. It gives a quick reading and is fine for a real estate transaction. But for a retest meant to assess long-term exposure, I lean toward a long-term radon test. An alpha track detector, left in place for ninety days to a year, averages out the daily and seasonal swings. That average is a more honest representation of what you are actually breathing.

There is also the continuous radon monitor, which plugs into an outlet and records hourly readings. These devices are more expensive but show you the peaks and valleys. If you suspect that radon spikes at certain times of day or during specific weather events, a continuous monitor can confirm it. For a thorough radon retest, especially after mitigation, I often recommend using both a long-term alpha track detector and a continuous monitor for the first week to catch any immediate red flags.

How to Read Your Retest Results

The action level of 4 pCi/L is the EPA benchmark, not a safety line. The agency itself says there is no safe level of radon. If your retest comes back at 3.8 pCi/L, you are technically below the action level, but many experts still recommend reducing it further. A radon mitigation system, such as soil suction radon reduction or a radon fan system, can typically bring levels below 2 pCi/L.

If the retest shows a number above 4 pCi/L, do not panic. It is a fixable problem. In Metro East Illinois, the homes I see in Belleville, Edwardsville, O'Fallon IL, and Collinsville almost always respond well to sub-slab depressurization. A single suction pipe through the slab, connected to a fan vented above the roofline, can drop radon levels by 80 to 99 percent. The key is to test after the installation to confirm the system is working. That final radon retest is what tells you the job is done.

Radon Retest and Real Estate Transactions

If you are buying or selling a home, a radon retest is often required, especially if the original test is more than two years old. Lenders and buyers want current data. A test from 2019 means nothing in 2024. The home may have been vacant, which can depress radon levels, or a new heating system may have changed the pressure dynamics. A fresh short-term radon test, conducted with the house closed up for at least twelve hours before the test begins, is standard practice.

I have been in homes where the seller insisted the radon was fine because a test from five years ago showed 2 pCi/L. When we retested, the reading was 7 pCi/L. That difference changed the negotiation entirely. A radon retest protects both parties and gives everyone a clear picture before closing.

Practical Tips for a Reliable Retest

To get a meaningful result, follow the same protocols you would for any radon test. Close all windows and doors at least twelve hours before starting the test. Keep them closed for the entire test period. Do not run window fans or whole-house ventilation systems. Place the radon detector in the lowest livable level of the home, away from drafts, heat sources, and exterior walls.

For a long-term radon test, the rules are looser because the test covers months. But you still want to avoid placing the alpha track detector in a spot where it gets direct sunlight, high humidity, or heavy vibration. A basement shelf or a corner of a finished rec room works well.

If you hire a professional, ask about their calibration and accreditation. Air Sense Environmental, for example, uses E-PERM electrets and continuous radon monitors that are calibrated annually. A good contractor will explain the results and walk you through the options if the levels are high.

The Bottom Line on Retesting

Radon is invisible, odorless, and tasteless. You cannot trust a single test forever. The geology under your home shifts, your house settles, and your lifestyle changes. A radon retest every two to three years is a small investment in your family's health. It takes a few days of your time and costs between twenty and fifty dollars for a mail-in kit, or a few hundred for a professional assessment. Compared to the cost of radon mitigation or the health risks of long-term exposure, that is a bargain.

If you live in Metro East Illinois, particularly in Belleville, Edwardsville, O'Fallon IL, or Collinsville, I encourage you to put a retest on your calendar. The soil here can be unpredictable, and the only way to know your exposure is to measure it. A radon retest is not an admission that something is wrong. It is the responsible way to stay informed about the air you breathe every day.