Short answer
EPA's action level is 4 pCi/L: at a confirmed result of 4 pCi/L or more, EPA recommends fixing the home, usually with a vent pipe and fan system. Between 2 and 4 pCi/L, EPA recommends considering a fix, and it says any radon exposure carries some risk, so the line is a decision point rather than a safe limit.
Next step: pick the right test for your home. Which test to use
The
The level applies to a confirmed result: one
Other bodies set their marks differently. WHO's advice is a national reference level of 100
What to do next: read your result with the interpreter, and if a confirmed level calls for a fix, find a certified
In a picture · 1 min read
EPA gives two numbers, not one. EPA recommends fixing a home when the radon level is 4
For scale, EPA estimates the average indoor radon level at about 1.3 pCi/L and puts outdoor air at about 0.4 pCi/L. Congress has set a long-term goal that indoor radon be no higher than outdoor levels. That goal is not yet technologically achievable in every case, and getting below 2 pCi/L is difficult, but most homes today can be brought down to 2 pCi/L or below.
At a glance · 1 min read
EPA's level applies to a confirmed result, not to a single quick test. Because radon levels vary from day to day and season to season, a
| What you tested | What decides it |
|---|---|
| One short-term test | Not enough on its own. If it is at or above 4 pCi/L, take a follow-up test. |
| First short-term result more than twice the action level | Take a second short-term test right away. |
| Follow-up long-term test (more than 90 days) | Fix the home if the long-term result is 4 pCi/L or more. |
| Follow-up second short-term test | Consider fixing if the average of the two is 4 pCi/L or more; the higher the results, the more certain you can be. |
| Home sale | Any of three short-term options: two tests at once, two in a row, or a continuous monitor, each run at least 48 hours. |
In a picture · 1 min read
The action level is a point on a sliding scale of risk. EPA's risk chart estimates how many people out of 1,000 could get lung cancer if exposed to a given level over a lifetime, and the numbers fall with the level but do not reach zero at 4, at 2 or even at the average indoor level.
EPA estimate, lifetime exposure
| Radon level | Could get lung cancer, per 1,000 | What to do |
|---|---|---|
| 20 pCi/L740 Bq/m³ | Smoked: About 260Never smoked: About 36 | Fix your home |
| 10 pCi/L370 Bq/m³ | Smoked: About 150Never smoked: About 18 | Fix your home |
| 8 pCi/L300 Bq/m³ | Smoked: About 120Never smoked: About 15 | Fix your home |
| 4 pCi/L150 Bq/m³ | Smoked: About 62Never smoked: About 7 | Fix your home |
| 2 pCi/L75 Bq/m³ | Smoked: About 32Never smoked: About 4 | Consider fixing between 2 and 4 pCi/L |
| 1.3 pCi/L50 Bq/m³ | Smoked: About 20Never smoked: About 2 | Average indoor radon level |
| 0.4 pCi/L15 Bq/m³ | Smoked: About 3Never smoked: No figure given | Average outdoor radon level |
At 4 pCi/L, EPA estimates that about 62 of 1,000 people who smoke and about 7 of 1,000 who never smoked could get lung cancer from a lifetime of exposure. At 2 pCi/L the estimates are about 32 and about 4. Smoking and radon together are an especially serious risk, which is why EPA's advice to people who smoke is to stop smoking as well as fix the home.
In a picture · 1 min read
The two agencies use different units and set their marks differently. EPA's 4 pCi/L is 148
Calculated by Radon411: figures marked calculated convert the publisher's unit at 37 Bq/m³ per pCi/L, EPA's factor: “1 pCi/L corresponds to 37 Bq/m3”. A becquerel is one atomic nucleus transforming each second. WHO sets reference levels for countries; EPA's level is a recommendation to fix a home.
Both rest on the same evidence about long-term exposure: WHO puts the rise in lung cancer risk at about 16 percent per 100 Bq/m3 increase in the long-term average, and treats the relationship as linear. EPA's 2 to 4 pCi/L range for considering a fix works out to about 74 to 148 Bq/m3 (our conversion, at 37 Bq/m3 per pCi/L), so WHO's 100 falls inside it.
At a glance · 1 min read
EPA's levels are recommendations to homeowners, not a law that forces a fix. What can be required depends on where you live: any
| Situation | What applies |
|---|---|
| Fixing your own home | EPA's guidance. Any system installed must meet your state's regulations; where a state has none, EPA recommends following its current voluntary consensus standards. |
| Hiring a contractor | Many states require radon professionals to be licensed, certified or registered. |
| Selling a home | Your state or local government may require disclosure of radon information to buyers. |
| New construction | Building codes in your state or local area may require radon-resistant construction features. |
State rules are summarized on our state radon programs page.
Questions · 1 min read
When a confirmed result reaches EPA's action level: one long-term test, or the average of two short-term tests, at 4 pCi/L or more. Between 2 and 4 pCi/L, EPA recommends considering a fix. Don't wait to act on a high result.
EPA recommends considering it: 3 pCi/L is inside the 2 to 4 range where EPA asks people to consider a fix, and EPA's position is that any exposure carries some risk. See what radon level is dangerous.
EPA does not recommend a fix below 2 pCi/L, and getting below 2 is difficult. The average indoor level is about 1.3 pCi/L.
Yes: EPA's action level is 4 pCi/L, and its guidance applies at 4 or more. A result of exactly 4.0, confirmed, is at the action level.
No. EPA recommends it; it does not order homeowners to fix. State and local rules may cover licensing, disclosure in a sale, building codes and how a system must be installed.
A national reference level of 100 Bq/m3, about 2.7 pCi/L, and no more than 300 Bq/m3, about 8.1 pCi/L, where 100 cannot be reached. Those conversions are ours, at 37 Bq/m3 per pCi/L.
Some radon reduction systems can lower levels by up to 99 percent, and most homes can be brought to 2 pCi/L or below. See does radon mitigation work.
How a radon test works, who can run one, and how to read the number it gives you.
How a professional radon test works, what it proves and whether it is worth it.
Read the guideWhat counts as high and how to bring them down.
Read the guideEPA's action level, WHO's reference level and what counts as acceptable.
Read the guide