Guide

Your Radon Result Came Back High. What Now?

The table

Result	What it means	Next step
Under 2 pCi/L	At or near typical indoor levels. The national average is about 1.3.	Nothing required. Retest every few years and after any major structural, foundation or HVAC change.
2 to 4 pCi/L	Below the action level. The EPA notes that reduction can still be considered in this range.	A long-term test gives the annual average. Worth doing if the short-term reading was near 4 or taken in summer.
4 to 8 pCi/L	Above the action level. Mitigation is warranted.	DEP: confirm with a 365-day long-term test for the annual average, or another 2 to 7 day short-term test, then mitigate.
8 to 20 pCi/L	Clearly elevated.	Confirm with a short-term test rather than a year-long one, then mitigate. Waiting twelve months at this level is not a good trade.
Over 20 pCi/L	Very high. Roughly fifteen times the national average.	Treat as urgent. Confirm quickly and mitigate promptly. Limit time spent in the lowest level in the meantime.

Why there is no safe level, and why 4 is still the number

Radon risk is understood as scaling with concentration and with duration of exposure, with no identified threshold below which it is known to be harmless. That is why the EPA does not call 4 pCi/L safe. It calls it the action level.

Part of the reasoning behind picking 4 is practical: it is a level that mitigation can reliably get below in ordinary houses. Systems routinely bring homes well under 2. The EPA's own guidance says you may want to consider reduction between 2 and 4, which is an acknowledgement that the line is a decision point rather than a biological boundary.

What this means practically: do not treat 3.8 as a clean bill of health, and do not treat 4.2 as an emergency. Both are the same situation, and the honest answer at either number is that a long-term test would tell you more.

When two tests disagree

This is common and it is not a sign that somebody made a mistake. A February short-term test and a July short-term test in the same house measure genuinely different conditions. So do two tests a week apart if a storm system moved through during one of them.

• Both above 4: mitigate. No further confirmation is buying you anything
• Both below 4: no action required, though a long-term test is cheap reassurance if either was close
• One above, one below: a 365-day long-term test settles it properly
• One above, one below, and you are under a transaction deadline: take the higher number seriously, because that is how the other side will read it
• Wildly different results, such as 3 and 15: check whether closed-house conditions held and where each device sat. A test disturbed midway is not a data point

What mitigation will realistically achieve

A correctly designed active sub-slab depressurization system generally brings a house well below the action level, frequently below 2 pCi/L, and often close to outdoor levels. That is the outcome to write into the contract: a guaranteed post-mitigation result stated as a number, with a defined remedy if it is not met.

A very high starting number does not usually mean a more expensive system. It more often means the same system with a better-placed suction point, or occasionally a second one. Price tracks foundation complexity, not the reading. See what it costs.

What not to do

• Do not buy an air purifier for this. HEPA and carbon units do not meaningfully reduce radon gas concentration
• Do not rely on sealing cracks on its own. Sealing is a supporting step, not a fix, because you cannot find every opening
• Do not open windows as a strategy. It works while they are open, in a Pennsylvania winter that is not a plan, and it invalidates any test running at the time
• Do not hire an uncertified installer. In Pennsylvania that is not a discount, it is an illegal transaction. See what a homeowner may legally do
• Do not skip the post-mitigation test. The number is the deliverable

Next: how the standard system works, what changes for an awkward foundation, and how to check a contractor's DEP certification.

Common questions

Is 4 pCi/L a safety cliff?

No. There is no threshold below which radon is known to be harmless; risk scales with concentration and duration. 4 pCi/L is the level at which the EPA says action is warranted, chosen partly because reliably getting below it is achievable, not because 3.9 is safe and 4.1 is not.

My two tests disagree. Which do I believe?

Neither on its own. Short-term results swing with season and weather. If both are above 4, mitigate. If one is above and one below, a long-term test settles it, unless you are on a transaction deadline, in which case take the higher number seriously.

Do I have to leave the house?

No. Radon is a long-term exposure risk, not an acute one. Even a very high result is a reason to act in weeks, not to evacuate. Reduce time spent in the lowest level while you sort it out if the number is extreme.