How to Test Home for Radon the Right Way

A home can look clean, dry, and well maintained and still have a radon problem. That is what makes this issue easy to miss during a typical walk-through. If you are wondering how to test home for radon, the key is to use the right test, place it in the right area, and follow the testing conditions closely enough that the result means something.

Radon is a naturally occurring radioactive gas that forms in soil and rock. It can enter a house through cracks in the foundation, sump pits, gaps around pipes, and other openings where the home meets the ground. You cannot see it or smell it, which is why testing is the only reliable way to know whether a home has elevated levels.

Why radon testing matters

Radon exposure is a health issue, not just a property issue. Long-term exposure to elevated radon levels increases the risk of lung cancer, and the risk is higher for smokers. Because the gas can build up indoors over time, even a newer home or a home that appears tightly built can test high.

In real estate, radon testing also helps buyers and sellers avoid surprises. A test can affect repair discussions, mitigation planning, and how comfortable a buyer feels moving forward. For current homeowners, it provides a clearer picture of indoor air conditions and whether a mitigation system should be considered.

How to test home for radon: start with the right type of test

The first decision is whether you need a short-term test or a long-term test. Both have value, but they serve different purposes.

A short-term test usually runs from 48 hours up to 90 days, depending on the device. This is the most common option during a home sale because it gives a faster answer. If you are on a contract timeline, short-term testing is usually the practical choice.

A long-term test remains in place for more than 90 days. This can give a better picture of average radon exposure over time because radon levels can change with weather, ventilation, and season. If you are not under a deadline and want the most representative reading for daily living conditions, long-term testing is often the better tool.

There is a trade-off here. Short-term tests are faster, but they can be more affected by temporary conditions. Long-term tests are more informative, but they are not helpful when you need an answer in a few days.

Where to place a radon test kit

Placement matters more than many homeowners expect. A poorly placed test can give a misleading result.

The test should be set in the lowest livable level of the home. In many houses, that means the basement if it is finished or regularly used. If the basement is unfinished and not used as living space, the first floor may be more appropriate, depending on the reason for testing. During a real estate transaction, the standard approach is usually to test the lowest level that could be used by occupants.

The device should not go in a kitchen, bathroom, laundry room, closet, crawl space, or near windows and exterior doors. It also should not be placed next to a draft, fan, high-heat source, or direct sunlight. A central area of the room, following the manufacturer's placement instructions, is usually best.

Height can matter too. Many kits need to be placed at least 20 inches above the floor, away from walls and other objects. The instructions that come with the kit should always be followed closely because different devices may have slightly different requirements.

Closed-house conditions are part of a valid test

One of the most common mistakes in radon testing is ignoring closed-house conditions. For many short-term tests, windows should remain closed and exterior doors should be kept shut except for normal entry and exit. These conditions usually need to begin at least 12 hours before the test starts and continue during the test period.

Why does that matter? Because opening windows changes air pressure and ventilation patterns inside the home. That can reduce or alter radon concentrations enough to make the result less reliable. If the goal is to understand what the home is actually trapping under normal occupied conditions, the test needs consistency.

This is especially relevant in areas like Chicago, where homes experience large seasonal swings. Winter heating, summer air conditioning, and shoulder-season window use can all affect indoor pressure and airflow. A properly controlled test helps reduce those variables.

DIY kit or professional radon test?

Homeowners often ask whether a store-bought kit is enough. Sometimes it is. A quality DIY kit can be a reasonable option if you are testing your own home, you are not under a real estate deadline, and you are comfortable following instructions exactly.

That said, professional testing has clear advantages. A trained inspector knows where to place the device, how to avoid invalid conditions, and how to document the process. Professional equipment may also provide continuous monitoring that shows fluctuations over the testing period, which can be useful if there is a question about the result.

For a real estate transaction, professional testing is often the better choice because it creates a clearer record and reduces the chance of a disputed result. It can also be helpful when a buyer wants an independent, third-party assessment rather than relying on a kit handled by the seller or occupant.

What radon level is considered high?

In the United States, 4.0 picocuries per liter, written as pCi/L, is the EPA action level. If a home tests at or above that level, mitigation is generally recommended.

Levels between 2.0 and 4.0 pCi/L deserve attention too. There is no completely risk-free radon level, so some homeowners choose to reduce radon even below the action threshold, especially if they plan to stay in the home long term.

If your short-term result is close to 4.0 pCi/L, the next step may depend on the situation. In a home purchase, a follow-up test or mitigation discussion may happen quickly. In a home you already own, a long-term test may help confirm the average level before making a larger decision.

What happens if the test result is elevated?

A high result does not mean the house is unsafe to enter immediately, and it does not mean the deal should fall apart. It means the home needs a practical next step.

The usual solution is a radon mitigation system, often called active soil depressurization. In simple terms, this system uses a fan and vent piping to draw radon from beneath the home and exhaust it above the roofline before it accumulates indoors. These systems are common, and when properly installed, they are often very effective.

After mitigation, the home should be retested to confirm the system is reducing radon to an acceptable level. Testing is also a good idea after major renovations, foundation work, or changes to heating and ventilation, since those conditions can affect radon entry and air movement.

Common mistakes when testing for radon

A bad radon test is worse than no test at all because it creates false confidence. The most common problems are placing the device in the wrong location, opening windows during the test, running the test for the wrong duration, or using a kit past its expiration date.

Another issue is assuming one old result tells the whole story forever. Radon levels can change. A house that tested acceptably years ago may test differently now due to settling, weatherization, HVAC changes, or shifts in how the basement is used.

It is also a mistake to assume only older homes have radon. Age, style, and visible condition do not reliably predict whether a home will test high. New homes, renovated homes, and homes with no obvious foundation issues can still have elevated radon.

When should you test?

If you are buying a home, test during the inspection period. If you already own the home and have never tested, now is a good time. You should also consider retesting every few years, after installing a mitigation system, after major structural changes, or if you begin using a lower level of the home more often.

For homeowners who want the clearest understanding of indoor conditions, pairing radon testing with a broader inspection mindset makes sense. Moisture issues, ventilation patterns, insulation performance, and foundation details can all affect how a house behaves. That is part of why companies like Attentive Home Inspection approach diagnostics with careful documentation and client education, not just a single number on a report.

The most helpful way to think about radon testing is this: it is not about creating fear. It is about removing guesswork. A clear, properly performed test gives you something every homeowner and buyer needs when making decisions about a property - reliable information.