Home Radon Testing Guide: Kit Placement, Results, and Mitigation

Radon has no color or smell, so you cannot tell whether it is in your home without measuring it. A newer home is not automatically protected, a house without a basement is not exempt, and a neighbor’s low result does not predict yours. Testing matters even more when you plan to use a basement as a bedroom or office, buy or sell a home, or complete work that changes the foundation, windows, insulation, or ventilation.

The Centers for Disease Control and Prevention (CDC) describes short-term tests as measurements lasting 2 to 90 days and long-term tests as measurements lasting more than 90 days. A short-term test provides a relatively quick snapshot. A long-term test captures more seasonal and day-to-day variation and is more representative of an annual average. The U.S. Environmental Protection Agency (EPA) recommends fixing a home at 4 picocuries per liter (pCi/L) or higher and considering steps to reduce radon between 2 and 4 pCi/L. There is no known completely safe level, so the result should guide a next step rather than be treated as a simple pass-or-fail grade.

This article provides general U.S. home-maintenance and radon information. It does not diagnose an individual health risk or replace medical, real-estate, legal, or engineering advice. Discuss health concerns with a qualified health professional and check current state and local rules for rental or transaction obligations. High results, confirmation testing, and mitigation work are best handled with a properly credentialed professional recognized in your area.

Start with the basics: how radon enters a home

Radon is a naturally occurring radioactive gas released from soil, rock, and groundwater. Pressure differences between the soil under a house and the indoor space can draw radon through foundation cracks, floor-to-wall joints, utility penetrations, sump openings, and crawl spaces. Groundwater can also be a route in some homes with private wells, but testing the indoor air is generally the first step.

Two similar homes can produce different readings because their foundations, soil, drainage, ventilation, heating patterns, and weather conditions differ. EPA radon-zone maps show regional potential; they do not predict the result at a specific address. Do not assume that your home is clear because the county is shown as lower potential, or that it must be high because a neighbor had a high result. Test the space where your household actually lives.

Radon exposure is not something you identify through an immediate odor, headache, or other warning sign. The CDC explains that long-term exposure to elevated radon can raise lung-cancer risk and identifies radon as the second leading cause of lung-cancer deaths in the United States. Current or former smoking can further increase risk. A high home test is not a diagnosis, however. Instead of removing the test, panicking, or leaving windows open indefinitely, validate the measurement and choose a durable reduction strategy.

Choose the right type of test

Short-term test: a practical first look

Depending on the product, a short-term kit measures radon for 2 to 90 days. Many use a passive collector that you send to a designated laboratory. Read the package carefully to learn whether laboratory analysis and return shipping are included. A short-term kit is a reasonable first step if the home has never been tested or if you want an initial result before committing to a longer measurement.

Short-term results can be influenced by weather and building operation. Record major storms, unusually strong wind, construction that required doors or windows to stay open, or a major change in heating and cooling. If you could not maintain the conditions required by the instructions, do not force an interpretation. Repeat the test correctly or arrange a professional measurement.

Long-term test: a better picture of normal living conditions

A long-term device stays in place for more than 90 days, capturing more of the home’s seasonal changes and normal ventilation patterns. If you own the home and do not face a transaction deadline, this type of result can better represent the annual average. It may also help when a valid short-term result falls near a decision point, such as the 2-to-4 pCi/L range.

Continuous monitor: use the trend without chasing hourly numbers

An electronic continuous radon monitor can show changes over time and may help you observe patterns related to HVAC use, open doors, or weather. Do not judge the whole home from a single hourly reading on a consumer display. Follow the manufacturer’s placement, warm-up, calibration, and measurement-period directions. For a real-estate transaction or repeatedly high readings, consider an independent credentialed tester.

When professional measurement makes sense

A purchase contract sets a deadline or specific test protocol.
A short-term result is high, invalid, or very different from a second test.
The house has multiple foundation areas, both a basement and crawl space, or several lower-level living rooms.
You need to verify that an existing mitigation system still works.
The property is a rental, child-care setting, school, or multifamily building with more complex rules and responsibilities.

EPA directs homeowners to state radon programs for help finding test kits and qualified measurement or mitigation providers. Do not rely only on an advertisement that says “certified.” Verify any license required by the state or a credential from a national proficiency program recognized by EPA.

Pre-test planning checklist

Before ordering a kit, sketch the home’s lower levels and identify the rooms people actually use. This small step prevents many placement errors. Record:

Foundation types and sections: basement, slab, crawl space, or a combination
The lowest floor currently occupied or likely to be occupied
Bedrooms, family rooms, offices, and playrooms where people spend substantial time
Windows, exterior doors, supply and return vents, ceiling fans, and dehumidifiers
Recent foundation, insulation, window, HVAC, drainage, or remodeling work
Sump pits, floor drains, mechanical rooms, fireplaces, and private wells
The kit expiration date, laboratory fee, registration requirement, and return deadline

If you also want to document air leaks and ventilation, use the fall home energy audit checklist to inspect doors, windows, attic areas, and HVAC airflow. Air sealing can change pressure and airflow, so test before a major project to establish a baseline and test again after the work is complete.

How to place a short-term kit in eight steps

Read every instruction before opening the device. Test duration, indoor conditions, placement height, and return procedure can vary. The approved directions supplied with your kit take priority over a general article.
Select the lowest level used as living space. If a finished basement is a bedroom, office, playroom, or family room, start there. A rarely entered mechanical corner is less useful than the space where people spend time.
Pick a representative room. CDC guidance describes placing the device on the lowest level, about three feet above the floor and in the middle of the room. Follow the kit’s specific permitted height and clearance instructions if they differ.
Avoid interference. Keep the device away from windows, exterior doors, supply or return vents, fans, fireplaces, direct sunlight, high-humidity kitchens or bathrooms, and places where it could be disturbed.
Document the start. Photograph and record the kit number, exact room and location, floor, start date and time, and relevant indoor conditions.
Maintain normal living conditions. Follow the kit’s door and window requirements. Do not ventilate unusually just to lower the result, and avoid construction or other activities that make the test unrepresentative.
End the test on time. Stay within the product’s approved exposure period and record the exact stop date and time.
Seal, register, and ship promptly. Complete every required field and check whether the lab has a receipt deadline. Use tracking when appropriate and watch your spam folder for the report.

Example: Imagine a basement with laundry and a boiler on one side and a home office used every weekday on the other. Do not put the kit on the floor beside the boiler or on top of the washing machine. Place it on a stable table or shelf in the office, away from the window, door, and vent, at the height allowed by its instructions. Take one wide photo showing the room and device location, then create reminders for both the stop time and the shipping deadline.

What to do in a complicated floor plan

One kit may not represent every area of a large or structurally divided house. Ask your state radon program or a measurement professional how many locations are appropriate if the home has separate foundation zones, a basement plus a slab addition, or several occupied rooms on the lowest level. In an apartment or condominium, the starting point is generally the lowest occupied level inside your unit, but you should also review building policies and any plan for common areas.

Do not simply toss a consumer kit into a crawl space. That may measure the foundation cavity instead of household exposure. Test the occupied area; if results are high, a mitigation professional can evaluate the entry routes and pressure beneath each foundation section. Boiler rooms, humid bathrooms, kitchens, and locations beside a clothes dryer are also poor substitutes for a representative living space.

How to read the laboratory report

Exterior radon mitigation piping and a foundation soil-gas exhaust system on a U.S. home — A radon mitigation system can collect soil gas below the foundation and exhaust it outdoors through a pipe and fan.

A report normally shows an average concentration in pCi/L, the measurement period, and laboratory information. Before focusing on the number, decide whether the test was valid. Was the kit exposed for the correct period? Were start and stop times accurate? Was it returned promptly? Did anyone leave windows open for long periods or perform construction? A low number from an invalid test does not provide reliable reassurance, and an invalid high number should not be the sole basis for signing a mitigation contract.

At or above 4 pCi/L

EPA and CDC guidance supports taking action to reduce radon at this level. Confirm that the test procedure was sound, then contact a qualified measurement or mitigation professional listed through your state program. A follow-up measurement may be appropriate depending on the situation, but do not leave a credible high result unresolved. Ask multiple providers to evaluate the same conditions and deliver a written scope that includes post-installation testing.

From 2 pCi/L to below 4 pCi/L

EPA recommends considering ways to reduce radon in this range as well. A long-term test can provide a better estimate of annual exposure, or a professional can discuss practical reduction options for the home’s foundation and living areas. Smoking history or substantial time spent on the lowest floor may be reasons to discuss personal concerns with a health professional, but a home reading alone cannot calculate an individual diagnosis.

Below 2 pCi/L

A lower result is not a permanent exemption from future testing. CDC recommends testing when buying or selling, before and after renovations, and before someone begins spending more time on a lower level. Test again after foundation repair, sump work, major HVAC changes, window and insulation projects, or converting a basement into a bedroom. Follow any retesting schedule recommended by your state radon program.

Questions to ask a mitigation contractor

In many existing homes, active soil depressurization uses a pipe and fan to collect soil gas beneath the foundation and exhaust it outdoors. A crawl space may need a sealed membrane connected to the system. Homes with several foundation sections may require more than one suction point. Sealing cracks can help a system work, but caulk by itself should not be assumed to provide lasting radon control. Opening windows may temporarily change the reading, but it is not a dependable substitute for a permanent system.

Compare written scope, qualifications, and verification—not just the bottom-line price. Ask each contractor for:

The company’s and field technician’s state license or recognized credential number
The recommended system type and the reason for the proposed number of suction points
The scope for the fan, pipe, electrical connection, roof or wall penetrations, and crawl-space membrane
Confirmation that the exhaust location will be appropriately separated from windows, doors, and air intakes
A visible system indicator and instructions for the homeowner’s monthly check
Plans for fan noise, condensation, freezing conditions, and weather exposure
The timing and responsibility for an independent post-mitigation radon test
Workmanship and fan warranties, maintenance, and replacement procedures
Who obtains permits and completes any required electrical work

Comparison example: Contractor A writes only “install one fan.” Contractor B separates the pressure diagnostic, two foundation sections, pipe route, outdoor exhaust point, system indicator, post-installation test, and warranties. Before selecting either quote, ask both companies to address the same checklist. Because every foundation and market is different, do not treat an unverified national average price as your budget. Obtain site-specific written estimates.

After the system is installed

Save the contract, credentials, system drawing, fan model, warranties, and before-and-after photos together.
Retest radon under the installer’s specified conditions and time frame to verify that the concentration decreased.
Photograph the normal position of the system indicator and inspect it visually every month.
If the fan sound disappears or the indicator changes, contact the provider rather than repeatedly switching the system on and off.
Seasonally inspect roof, siding, and pipe penetrations for leaks or damage.
Test again after an addition, foundation work, or a significant HVAC change.
When selling, organize system records and test reports for disclosure under current local rules.

A radon fan and pipe should not interfere with other safety systems. Use the home fire escape plan checklist to review smoke and carbon-monoxide alarms and two exit routes from sleeping areas. A radon monitor is not a smoke alarm or a carbon-monoxide alarm; each risk requires its own equipment and response.

Special considerations for renters, landlords, buyers, and sellers

Renters

Review the lease, then ask the owner or property manager in writing for the latest report, test location, and mitigation maintenance history. Check whether approval is required before placing your own kit, and keep the original report and photos. Repair duties and timelines after a high result vary by jurisdiction, so confirm current requirements with your state, city, or county housing or health agency.

Landlords

Base the test plan on the lowest occupied spaces tenants actually use. Keep the laboratory report and location record instead of sending only a text-message summary. In a multifamily building, do not infer every unit’s condition from one result; ask the state program or a qualified professional for an appropriate sampling plan. If a mitigation system is present, show tenants the system indicator and provide a maintenance contact.

Home buyers and sellers

A short transaction schedule makes a clear written protocol essential. The contract should address who selects the tester, how tampering is monitored, and what happens after a high reading—such as follow-up testing, mitigation, or another negotiated remedy. EPA recommends a qualified tester for a real-estate transaction. An existing fan is not proof of a current low level; review recent results and verify operation.

Ten common mistakes

Predicting your result from a neighbor’s. Soil, foundations, and airflow vary by address, so test your own home.
Putting the kit on the floor, windowsill, or beside a vent. Follow the device instructions in a representative living room.
Relying on memory for the exposure period. Set stop and shipping reminders when the test begins.
Opening windows to improve the number. An artificial condition does not describe normal exposure.
Hiring the first contractor immediately after one result. Validate the test and compare credentials and matching written scopes.
Assuming caulk alone solves the problem. Sealing may support a designed mitigation system but is not a universal solution.
Assuming a quiet fan is operating. Check the system indicator and verify performance with testing.
Skipping the post-installation test. Measurement is how you confirm that the system reduced radon.
Keeping an old result after major remodeling. Changes to foundations and airflow call for another test.
Confusing radon with carbon monoxide. They have different sources and require different detectors and controls.

Action checklist

□ Identify the lowest occupied floor and the rooms used most often.
□ Check the state radon program for kits or qualified professionals.
□ Verify the kit expiration date, laboratory fee, registration, and return process.
□ Place the device at the approved height and location under the required indoor conditions.
□ Save the start and stop times and a photo of the location.
□ Review test validity as well as the reported concentration.
□ At 4 pCi/L or higher, seek qualified mitigation guidance.
□ Between 2 and 4 pCi/L, consider a long-term test or reduction options.
□ Compare contractor credentials, design, verification testing, and warranties.
□ Schedule a post-mitigation test and monthly system-indicator check.
□ Plan to retest after construction or a change in lower-level use.

Frequently asked questions

Do I need to test if my home has no basement?

Yes. Radon can enter through slab cracks, utility penetrations, crawl spaces, and other openings. EPA recommends testing all homes. In a home without a basement, test the lowest occupied floor according to the kit instructions.

Is a new home automatically radon-free?

No. Even if the builder used radon-resistant features, measure the finished home under occupied conditions. Review construction documents to learn whether a passive vent can accept a fan if needed, but do not substitute that paperwork for a test.

Can I test only in winter?

You can test year-round. Seasonal conditions can affect results, which is why a short-term measurement is a snapshot and a long-term device can better represent the annual average. Avoid periods when extreme weather or construction makes it impossible to follow the kit instructions, or consult a professional.

If the result is 3.9 pCi/L, can I ignore it?

No single decimal creates a completely safe side of a line. EPA and CDC guidance supports considering reduction between 2 and 4 pCi/L, and there is no known safe radon level. Review test quality, consider longer measurement, and discuss reasonable reduction options for the house.

Will opening windows solve high radon?

Ventilation may lower a reading temporarily, but it depends on weather and occupant behavior and is not reliable as a permanent control. A qualified professional can design a durable system for the foundation.

Does an air purifier remove radon?

Do not treat a typical air purifier as a replacement for radon mitigation. Proven approaches usually control soil gas before it enters and exhaust it outdoors through a building-specific design. Follow EPA and state-program guidance rather than a product claim.

Does a mitigation system eliminate the need for future tests?

No. Test after installation to verify performance, watch the system indicator, and follow the recommended retesting schedule. Fans are mechanical and electrical equipment and may eventually fail or require replacement.

Can drainage and radon work affect each other?

Sump openings, foundation cracks, and crawl spaces can matter to both moisture management and radon entry. Never alter a radon pipe to solve a water problem. Document gutters, grading, and sump conditions with the fall home drainage checklist, then coordinate the radon, waterproofing, and plumbing scopes so one system does not compromise another.