Radon testing is the only way to learn your home’s level, and it takes little effort. A short-term kit sits in the house for a few days, then goes to a lab. EPA’s radon page says, “All homes should be tested for radon.” A neighbor’s result can’t stand in for yours, and neither can EPA’s zone map.
This page takes testing in order: choose a test, run it, follow up, then act on the number, with a deeper guide at each step. Results come in pCi/L, picocuries per liter of air.
The tests at a glance
| Test | Time in the home | What it suits | Dated prices |
|---|---|---|---|
| Short-term kit, sent to a lab | 2 to 90 days by EPA’s definition. Many kits run only a few days | A first test, or a quick second one | $20, all costs included, National Radon Program Services at Kansas State University (K-State), read 4 Nov 2026. New Jersey adds a $10 fee |
| Long-term kit, sent to a lab | More than 90 days. The K-State kit runs 3 to 12 months | Your year-round average | $30, all costs included, K-State, read 4 Nov 2026 |
| Professional test | At least 48 hours | A home sale, or when you want someone else to run it | $150 to $800, Bob Vila, a published estimate from 2022, so treat it as old |
| Home digital monitor | As long as you leave it on | Watching for changes | $100 to $200 on average, Wisconsin, revised 21 Oct 2026 |
Check any price or offer before you rely on it.
Who should test, and when
EPA’s Citizen’s Guide (2025 cover) is narrower: EPA and the Surgeon General “recommend testing all homes below the third floor”. Levels “can vary greatly from home to home”, and EPA says its zone map “should not be used to determine if individual homes need to be tested“.
On timing, sources differ. ANSI/AARST MAH-2023, the consensus standard for measuring radon in homes, advises testing at the earliest chance and says homes can be tested at any time of year. Massachusetts says to test between November 1 and March 31, and Minnesota calls the heating season the best time. So don’t put off a first test to wait for winter. If a summer result is below 4 pCi/L, a second test in the heating season is a reasonable follow-up.
Run a first test
EPA’s steps start with a short-term test. What decides whether you can trust the number is the room, the windows and the clock:
- Close up. Keep windows and outside doors shut for at least 12 hours beforehand and during the test, “except for normal entry and exit”.
- Pick the spot. The lowest lived-in level, in a room used regularly but not your kitchen or bathroom, at least 20 inches above the floor.
- Time it. Leave the kit out as long as the package says, never under 48 hours, and write down the start and stop times.
- Mail it right away. A late kit can spoil the reading.
Our guide on how to test for radon covers the exact distances, a forgotten 12 hours, storms and large homes.
For a kit, start with your state radon office. EPA says, “Free test kits are sometimes available from local or county health departments, or from state radon programs.” Offers change with the money behind them: as of 4 November 2026, federal radon funding generally runs on a stopgap through 11 December 2026, and the President’s budget proposed ending EPA’s state radon grants.
How long it takes
EPA says all radon tests “should be taken for a minimum of 48 hours”, and some need longer. Mail and lab time come on top. In our example, using the K-State kit’s lab time and assuming two-day shipping, a 48-hour test gives a result 9 to 11 days after you open the kit. EPA’s Citizen’s Guide says within a few weeks.
Too long can be as bad as too short. The 2025 sheet for the K-State charcoal kit calls a test under 48 hours or over 168 hours invalid, and that kit must reach the lab within 10 days of the test ending. Plan the end before you start. Our page on how long a radon test takes has a sample calendar and what can void a test.
Follow up: short test or long test
If a first short-term result is 4 pCi/L or higher, EPA says to “take a follow-up test (Step 2) to be sure”. By our arithmetic, a second short test takes about three weeks in all by mail. It’s EPA’s route “If you need results quickly”, and if the first result is more than twice 4 pCi/L, “you should take a second short-term test immediately”. A long-term test takes close to four months in all, and is “more likely to tell you your home’s year-round average radon level”.
The choice matters most near 4, where short tests are least certain. If two short tests average 4.1, EPA says “there is about a 50% chance that your year-round average is somewhat below 4 pCi/L.” If a long test and a short test disagree, go by the long test. One trap: a 91-day test from June to August counts as long-term but misses winter. Our comparison of short-term and long-term radon tests shows which fits which situation.
Where a home monitor fits
A home monitor is good for watching how a level moves over weeks and months, and weaker for a decision. In a UK Health Security Agency study at about 4.5 pCi/L, one of seven monitor types had an error under 10% and the others were 20% or worse. That was a UK lab test, not one in US homes. MAH-2023 requires a device listed by a local program, NRPP, NRSB or an equivalent for a mitigation decision. EPA says that if a monitor finds a level above 4 pCi/L, “you may wish to use a long-term test or consult a Radon professional.” So treat a monitor as a screen, and confirm with a lab test or a professional one. Our guide to radon monitors compares types and public specs.
Three cases with their own rules
Buying or selling
EPA’s Home Buyer’s and Seller’s Guide (March 2024) gives three options for a sale, each for at least 48 hours: two short-term passive tests at the same time, one followed straight after by an identical second test, or one continuous monitor. The test goes in the lowest level that could be used regularly, finished or not, and some states add rules. Our page on radon testing and home inspections covers the contract side.
A home with a radon system
Test with the system running. EPA’s Consumer’s Guide (2025 cover) says the fan should “NEVER be turned off”. After a new system goes in, it calls for a two- to seven-day test within 30 days of installation, no sooner than 24 hours after the system starts. After that, retest at least every two years, which is part of the system upkeep schedule.
A private well
Air comes first. The Citizen’s Guide says to test the air, and if high levels turn up and the home has a private well, to call the Safe Drinking Water Hotline about testing the water. An air kit won’t test water, so see radon in water.
What to do with the number
Our radon test result reader takes your number and test type and shows the matching step. These are EPA’s steps for a home that isn’t being sold:
| What you have | What EPA says |
|---|---|
| Long-term test, 4 pCi/L or more | “Fix your home if your long-term test result is 4 pCi/L or more.” |
| Two short-term tests averaging 4 pCi/L or more | “Consider fixing your home if the average of your first and second test is 4 pCi/L or higher” |
| Between 2 and 4 pCi/L | “Consider fixing if your level is between 2 and 4 pCi/L” |
| Any result below 4 pCi/L | “Even if your test result is below 4 pCi/L, you may want to test again sometime in the future.” |
EPA isn’t fully consistent on two short tests: the Citizen’s Guide says “consider fixing”, while the Consumer’s Guide recommends fixing. Either way, 4 is a decision point, not a safety line: “Radon levels less than 4 pCi/L still pose a risk, and in many cases may be reduced.” See what EPA says about radon levels.
What to do next
EPA’s advice at the front of the Citizen’s Guide is short: “Test your home for radon—it’s easy and inexpensive.” Then: “Fix your home if your radon level is 4 picocuries per liter (pCi/L) or higher.” If you don’t have a number yet, a short-term kit is the next step. Before you buy one or book a tester, ask:
- Does the price cover lab analysis and return shipping?
- What’s the shortest and longest allowed test time for this device?
- How soon must it reach the lab, and how long do results take?
- Does my state radon office offer kits right now?
Radon Handbook sells nothing and refers no one. This page is general information, not medical, engineering or legal advice. Your kit’s instructions and your state’s rules come first.
Sources checked on 4 November 2026.
