Radon Levels
Radon level of 20 pCi/L: what it means
Try it
Move a reading around 20 pCi/L
The reading starts at 20 pCi/L. Slide it to see where EPA's guidance changes and how far this number is from each line.
Read a result for 20 pCi/L
Starts at 20.0 pCi/L, this page's reading
EPA’s own thresholds, as its guidance states them.
EPA’s reading of 20.0 pCi/L
At or above 4 pCi/L
- Under 20 to 1.9 pCi/L
- 2 to 4consider a fix
- 4 and aboveEPA says fix it
This result is at or above 4 pCi/L. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. That is 16.0 pCi/L above EPA's action level, 5.0 times it.
Short answer
A radon level of 20 pCi/L is very high: five times the action level, and the top row of EPA's risk chart. Confirm it with a second short-term test right away and then fix the home.
Next step: pick the right test for your home. Which test to use
Key takeaways
- 20 pCi/L is 5 times EPA's 4 pCi/L action level.
- More than twice the action level: confirm right away, then fix.
- EPA estimates the average U.S. home at about 1.3 pCi/L; 20 pCi/L is 15.38 times that.
- Confirm a first short-term result this high with a second short-term test immediately.
Where it sits
Is a radon level of 20 pCi/L high?
The risk chart puts 20
- 740 Bq/m3
- 20 pCi/L in becquerels per cubic meter, the published figure.
- 5 times
- EPA's 4 pCi/L action level (calculated).
- 15.38 times
- The U.S. indoor average of about 1.3 pCi/L (calculated).
Read moreThree paragraphs and a table, 1 min
Readings in the 20s are fixable. Even very high levels can be reduced to acceptable levels, and the number and location of suction points a system needs depends partly on the strength of the radon source.
20 pCi/L is 50 times the outdoor average and about 15 times the average U.S. home, by our calculation. A 90% reduction brings 20 pCi/L to 2, within the up to 99 percent EPA cites for some radon reduction systems, which is why readings this high are still fixed to ordinary levels.
Where 20 pCi/L sits against EPA's and WHO's reference points
Against outdoor air (about 0.4 pCi/L)
50 times the outdoor average (calculated)Against WHO's recommended reference level (100 Bq/m3, 2.7 pCi/L)
Above itEPA's band
More than twice the action level: confirm right away, then fix
Other readings explained: 1 pCi/L, 2 pCi/L, 3 pCi/L, 4 pCi/L, 5 pCi/L, 6 pCi/L, 7 pCi/L, 8 pCi/L, 10 pCi/L, 12 pCi/L, 30 pCi/L, 100 pCi/L.
What to do
What to do about a radon level of 20 pCi/L
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. For a reading of 20 pCi/L, the steps come to this:
Steps for a reading of 20 pCi/L
Retest right away
20 pCi/L is 5 times the action level, more than twice it, so take a second short-term test immediately rather than wait for a long-term test.Check the first test
Improper testing may give inaccurate results; confirm the device, its placement and closed-house conditions.Fix the home
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Get estimates from qualified contractors; see radon mitigation.Test after the fix
No sooner than 24 hours and within 30 days after the system starts, then at least every two years.
Read moreA paragraph, 1 min
The full sequence of tests, from a first result to the decision to fix, is drawn on radon testing.
Health risk
The lung cancer risk at 20 pCi/L
EPA's risk chart has a row for 20 pCi/L. It estimates how many people out of 1,000 could get lung cancer if exposed to that level over a lifetime, separately for people who smoked and people who never smoked.
| Radon level | People who smoked | People who never smoked | What to do |
|---|---|---|---|
| 20 pCi/L (740 Bq/m3) | About 260 in 1,000 | About 36 in 1,000 | Fix your home |
Read moreTwo paragraphs, 1 min
At 20 pCi/L, the chart's lifetime estimate is about 260 in 1,000 people who smoked (250 times the risk of drowning), and about 36 in 1,000 who never smoked (35 times the risk of drowning). The comparisons in parentheses are the ones EPA prints beside the row.
Lung cancer risk is estimated to rise by about 16% per 100 Bq/m3 of long-term average radon. At 740 Bq/m3, a long-term average of 20 pCi/L, that comes to about 118% above the risk with no radon at all (our calculation, a population estimate, not a forecast for one person); a former smoker's risk may sit between the chart's two columns.
How sure
How certain is a reading of 20 pCi/L?
At 20 pCi/L the question is not whether the home is high but how high, since a day-to-day or seasonal swing cannot explain a reading this far above the
Read moreA note, 1 min
With a system
How much a radon system would lower 20 pCi/L
From 20 pCi/L, an active system at the low end of its typical range would leave about 10 pCi/L, still at or above the action level, so the test after installation decides whether the system is enough; at the high end, about 0.2 pCi/L. Our arithmetic on the published ranges, not a prediction for your house: radon levels in most homes can be reduced to 2 pCi/L or below.
| Technique | Typical reduction | From 20 pCi/L, about |
|---|---|---|
| Active suction: sub-slab, sump hole, drain tile, or a crawl-space membrane | 50 to 99 percent | 10 to 0.2 pCi/L |
| Passive sub-slab suction (no fan) | 30 to 70 percent | 14 to 6 pCi/L |
Read moreA paragraph, 1 min
Which technique fits depends on the foundation; see radon mitigation systems, and for cost, radon mitigation cost.
Situations
Where people meet a reading of 20 pCi/L
20 pCi/L in three common situations
20 pCi/L on a first test
Check how the test was run. Improper testing may yield inaccurate results and require another test, and disturbing the device or the closed-house conditions may invalidate the result.Designing a system for 20 pCi/L
With a strong radon source, the number and location of suction pipes matter, and the contractor may need to run diagnostic tests during the first phase of the installation.20 pCi/L after a mitigation system
As a post-mitigation result, 4.0 pCi/L or greater means fix the building, and with a system already installed, more work may be needed to lower the radon further. Many contractors guarantee to adjust or modify the system to reach a negotiated level.
Retest
When to retest after 20 pCi/L
20 pCi/L is five times the action level and the top row of EPA's chart. Take a second
| When | What to do |
|---|---|
| To confirm the first result | Immediately, with a second short-term test |
| After a system is installed | No sooner than 24 hours and within 30 days, with a two- to seven-day test |
| With a system in place | At least every two years |
| After a remodel | In the lowest lived-in area |
Show all 4 rows
Read moreA paragraph, 1 min
The general answer is on how often should I test for radon.
Questions
Radon level of 20 pCi/L: questions
Is 20 pCi/L of radon safe?
No. 20 pCi/L is at or above EPA's 4 pCi/L action level, where EPA recommends fixing the home once the result is confirmed.
Do I need radon mitigation at 20 pCi/L?
Yes, by EPA's guidance, once a long-term test or the average of two short-term tests confirms the level is 4 pCi/L or more; 20 pCi/L is 5 times that line.
What is 20 pCi/L in Bq/m3?
It is 740 Bq/m3, the figure EPA prints for it.
Should I buy a house with a radon level of 20 pCi/L?
A high level is fixable: from 20 pCi/L, an active system's typical reduction would leave 10 pCi/L or less. Buyers and sellers should discuss the timing and costs of radon reduction, and the contract can say when mitigation happens and who pays. See should I buy a house with radon.
Is 20 pCi/L in a basement different from upstairs?
Usually the basement reads higher. If 20 pCi/L came from a room upstairs, a basement half again as high would read 30 pCi/L, at or above the action level; a test belongs in the lowest lived-in level.
How long should I wait to retest after 20 pCi/L?
Do not wait: 20 pCi/L is more than twice the action level, and a first short-term result that high calls for a second short-term test immediately.
Can a home at 20 pCi/L get below 4?
Even very high levels can be reduced to acceptable levels. Across the 50 to 99 percent typical of active soil suction, 20 pCi/L would fall to somewhere between 10 and 0.2 pCi/L (our calculation), so the post-mitigation test is what tells you.