Guide
Short-Term vs. Long-Term Radon Testing: Which One Do You Need?
Updated
A short-term radon test stays in a home for 2 to 90 days (most often a few days to a week) and is the standard choice for real estate deadlines. A long-term test runs more than 90 days and accounts for seasonal swings in radon, giving a more accurate year-round picture. Both are read against the EPA's 4.0 pCi/L action level.
What a short-term test actually measures
A short-term test uses a charcoal canister, alpha-track detector, electret ion chamber, or continuous monitor placed in the lowest livable level of the home for 2 to 90 days, most commonly left in place a few days to about a week. Because radon levels naturally vary day to day and season to season, a single short-term test is a snapshot, not a year-round average. The EPA's own guidance notes that if a fast result is needed, a short-term test followed by a second short-term test can be used to decide whether to act.
What a long-term test actually measures
A long-term test, typically an alpha-track or electret detector, stays in place more than 90 days, which means it captures the seasonal swings that a short-term snapshot misses. Radon levels often run higher in winter, when a closed-up house exchanges less air with the outside, so a long-term test gives the closest thing to a true year-round average.
Which one fits your situation
A home sale almost always uses a short-term test because closings run on a deadline a 90-day test can't meet. Someone with no deadline who wants the most accurate possible number, especially in a house they plan to live in long-term, is better served by a long-term test, or by a short-term test followed later by a long-term one for confirmation.
Quick answers
FAQ
Can I just do a short-term test and be done with it?
Yes, and most people do. It's a reasonable snapshot, especially if the result comes back clearly below or clearly above the action level. Results close to 4.0 pCi/L are where a longer test or a second short-term test adds the most value.
Does the season I test in matter?
For a short-term test, yes, somewhat; winter results tend to run higher because the house is sealed up more. A long-term test smooths that out by design.
Which type does a real estate transaction use?
Almost always short-term, scheduled during the inspection period, because a 90-day long-term test doesn't fit a typical closing timeline.
Keep reading
Related guides
Is Radon Testing Required to Sell a Home in Illinois?
What Illinois law actually requires for radon on a home sale: the Radon Awareness Act, the disclosure rule, and what's just common practice.
DIY Radon Test Kit vs. Professional Testing: What's the Difference?
When a retail radon test kit is good enough, and when the situation calls for an IEMA-licensed professional instead.
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