Radon level of 3 pCi/L: is it bad?

On the risk chart, 3 pCi/L falls between the 2 pCi/L row (about 32 per 1,000 people who smoked, about 4 per 1,000 who never smoked) and the 4 pCi/L row (about 62 and about 7). Readings such as 3.1 or 3.6 sit in the same place.

About 110 Bq/m3

3 pCi/L in becquerels per cubic meter, at about 37 Bq/m3 per pCi/L (calculated).

75 percent

Of EPA's 4 pCi/L action level (calculated).

2.31 times

The U.S. indoor average of about 1.3 pCi/L (calculated).

EPA recommends considering a fix when the level is between 2 and 4 pCi/L. For a reading of 3 pCi/L, the steps come to this:

EPA's risk chart has no row for 3 pCi/L, so the table shows the rows either side of it. The chart estimates how many people out of 1,000 could get lung cancer if exposed to a level over a lifetime, for people who smoked and people who never smoked.

3 pCi/L from a short-term kit is a snapshot of a few days. The year-round average, which a long-term test comes closer to, can land either side of it: at 3 pCi/L, the home is 1 pCi/L from the action level, 33.33 percent of the reading, so an ordinary swing between seasons can carry it across.

From 3 pCi/L, an active system at the low end of its typical range would leave about 1.5 pCi/L, under 2 pCi/L; at the high end, about 0.03 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.

3 pCi/L is 1 pCi/L under the action level (our calculation), close enough to 4 that a short-term test is less definitive about which side of the line the year-round level falls. A long-term test, through winter if you can, when the heating runs day and night, is the follow-up that settles it.