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Test4 min read

Is a radon level of 4.1 considered high?

By Radon411 Editorial TeamUpdated How we research

Short answer

Yes, by EPA's measure: 4.1 pCi/L is just above EPA's 4 pCi/L action level, the point at which EPA recommends fixing a home. EPA's Citizen's Guide says short-term results that close to 4 are less definitive, so a follow-up test should confirm it before you decide.

Next step: pick the right test for your home. Which test to use

EPA's Citizen's Guide uses this very number as its example. It says are sometimes less definitive about whether or not your home is above 4 , which can happen when your results are close to 4 pCi/L: if the average of your two short-term test results is 4.1 pCi/L, there is about a 50% chance that your year-round average is somewhat below 4 pCi/L. It also says the closer the average of your two short-term tests is to 4 pCi/L, the less certain you can be about whether your year-round average is above or below that level.

A result just below the line would not mean safe either. EPA believes that any radon exposure carries some risk, and says even radon levels below 4 pCi/L pose some risk, and that you can reduce your risk of lung cancer by lowering your radon level.

What to do next: if 4.1 came from one short-term test, take a follow-up test, either a or a second short-term test. If a long-term test or the average of two short-term tests is at or above 4, EPA's guidance is to fix the home.

In a picture · 1 min read

Where 4.1 sits on EPA's scale

Scale of radon levels from 0 to 10 pCi/L marking EPA's 2 pCi/L level, where EPA says to consider fixing, and its 4 pCi/L action level, where EPA says to fix the home, with each mark also in Bq/m³.
EPA's two guidance levels; 4.1 pCi/L sits just above the 4 pCi/L action level.
Read this figure as text
  • Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
  • 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
  • At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
Read moreA paragraph, 1 min

EPA recommends fixing a home when the radon level is 4 or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. For comparison, the Citizen's Guide estimates the average indoor radon level at about 1.3 pCi/L, and about 0.4 pCi/L of radon is normally found in the outside air. EPA's page gives the action level as 150 in the metric unit; 4.1 pCi/L converts to about 152 Bq/m3 (calculated, at 37 Bq/m3 per pCi/L).

At a glance · 1 min read

What to do with 4.1, by the test that gave it

EPA's next step for a 4.1 pCi/L result, by test
Where the 4.1 came fromEPA's next step
One short-term testTake a follow-up test to be sure: a long-term test for your year-round average, or a second short-term test if you need results quickly
The average of two short-term testsConsider fixing your home if the average is 4 pCi/L or more; about a 50% chance the year-round average is somewhat below 4
A long-term testFix your home if your long-term test result is 4 pCi/L or more
A home sale, two tests or a continuous monitorFix the home if the average of the two tests is 4 pCi/L or more
Show all 4 rows
Read moreA paragraph, 1 min

Near the line, a answers best. The Citizen's Guide says a long-term test will give you a reading that is more likely to tell you your home's year-round average radon level than a , and that the higher your initial short-term result, the more certain you can be that a short-term follow-up is the right choice. See is a radon level of 5 bad and what 4 pCi/L means.

In a picture · 1 min read

What a fix achieves

Bar chart of EPA's radon risk estimates for people who smoked and people who never smoked: out of 1,000 people exposed over a lifetime, about how many could get lung cancer at 20, 10, 8, 4, 2, 1.3 and 0.4 pCi/L, from about 260 smokers at 20 pCi/L to about 3 at 0.4 pCi/L, with EPA's advice at each level.
EPA's lifetime risk chart, at 4 pCi/L and the levels around it.
Read this figure as text

EPA estimate, lifetime exposure

  • Out of 1,000 people who smoked
  • Out of 1,000 people who never smoked
About how many people out of 1,000 exposed over a lifetime could get lung cancer, by radon level
Radon levelCould get lung cancer, per 1,000What to do
20 pCi/L740 Bq/m³Smoked: About 260Never smoked: About 36Fix your home
10 pCi/L370 Bq/m³Smoked: About 150Never smoked: About 18Fix your home
8 pCi/L300 Bq/m³Smoked: About 120Never smoked: About 15Fix your home
4 pCi/L150 Bq/m³Smoked: About 62Never smoked: About 7Fix your home
2 pCi/L75 Bq/m³Smoked: About 32Never smoked: About 4Consider fixing between 2 and 4 pCi/L
1.3 pCi/L50 Bq/m³Smoked: About 20Never smoked: About 2Average indoor radon level
0.4 pCi/L15 Bq/m³Smoked: About 3Never smoked: No figure givenAverage outdoor radon level
  • Smoked: If you are a former smoker, your risk may be lower.
  • Never smoked: If you are a former smoker, your risk may be higher.
  • Reducing radon levels below 2 pCi/L (75 Bq/m3) is difficult.
  • Lifetime risk of lung cancer deaths, as EPA estimates it.
Show the whole figure
Read moreA paragraph, 1 min

The Consumer's Guide says that with today's technology, radon levels in most homes can be reduced to 2 pCi/L or below, and that some radon reduction systems can reduce radon levels in your home by up to 99 percent. It recommends a qualified radon contractor, and a test within 30 days of installation. See radon mitigation and what mitigation costs.

Questions · 1 min read

Questions about a 4.1 radon result

Is 4.1 pCi/L dangerous?

It is just above EPA's action level, where EPA recommends fixing a home. EPA says any radon exposure carries some risk, and the risk rises with the level and the time exposed.

Should I retest a 4.1 radon reading?

If it came from one short-term test, yes: the Citizen's Guide says to take a follow-up test, either a long-term test or a second short-term test, to be sure.

Is a radon test at 4.1 a reason not to buy a house?

EPA's Home Buyer's and Seller's Guide says you can fix a radon problem, and that even very high levels can be reduced to acceptable levels. See should I buy a house with radon.

What about a reading of 4.5, 4.8 or 4.9?

The guidance is the same for any result at 4 pCi/L or more: confirm a single short-term result with a follow-up test, then fix the home. The Citizen's Guide says the higher your short-term results, the more certain you can be that you should fix your home.

Is 4.0 high, or only above 4?

EPA's guidance is to fix at 4 pCi/L or more, so 4.0 is at the action level. See what does 4 pCi/L mean.

What is 4.1 pCi/L in Bq/m3?

About 152 Bq/m3, calculated at 37 Bq/m3 per pCi/L. EPA gives its 4 pCi/L action level as 150 Bq/m3.

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