Why Summer and Winter Radon Readings Disagree in Lincoln
September 9, 2026
A July test and a January test in the same Lincoln house can tell two different stories. Neither is wrong — but one of them usually deserves more weight.
Same House, Two Different Numbers
Test the same house in July and again in January and the reports can disagree by enough to change the decision. Neither test malfunctioned. Radon is not a fixed property of a building — it is a moving balance between soil gas coming in and fresh air diluting it, and both change with the weather.
The stakes are real in Lincoln because so many results land near the decision points: across 19,828 measurements in the Nebraska DHHS dataset, Lancaster County averages 3.6 pCi/L, just under the EPA's 4 pCi/L action level. That close to the line, a seasonal swing is often the difference between a report that says relax and one that says act.
What Winter Does to a House
Start with the stack effect. When the furnace runs, warm air rises and leaks out of the upper floors, and the makeup air replacing it gets pulled in low — some of it drawn from the soil through cracks, joints, and utility penetrations in the foundation. The colder it is outside, the stronger that pull.
The house also closes. Windows stay shut for months, so incoming radon is diluted far less than in April. Frozen or snow-covered ground caps the soil too, leaving gas fewer easy paths to open air — the basement becomes the path of least resistance.
What Summer Does Instead
Summer is less predictable. Open windows and door traffic dilute indoor air aggressively, and the stack effect weakens or even reverses on hot days. A whole-house fan can knock a reading down sharply — which is why short-term test instructions restrict fans and open windows.
But a tightly closed, air-conditioned house in a Nebraska heat wave is still a closed house, and some homes read high in August. Summer results simply scatter more: often lower than winter, sometimes not. That scatter is why a single summer number near the line deserves a follow-up rather than a shrug.
Which Number Should You Act On?
How to weigh results from different seasons:
- At or above 4 pCi/L in any season — the EPA recommends fixing a home at that level, and the calendar does not soften it. Heating season generally pushes readings up, not down, so a high summer result is rarely the year's worst.
- A summer result between 2 and 4 pCi/L — the range where the EPA recommends considering a fix. A retest under heating-season conditions, or a long-term test, shows what the house does the rest of the year; what a Lincoln result between 2 and 4 means covers this zone in detail.
- A winter result below 2 pCi/L — measured under the conditions that usually produce the year's highest readings, this is about as reassuring as a short-term test gets.
- Two tests that disagree — the one run under closed-house, heating-season conditions is generally the better stand-in for the months when the house is sealed up and occupied the most.
Put the Calendar to Work
If the timing is yours to choose, schedule short-term tests for the heating season, when the closed house shows its higher end. A long-term test that spans both seasons trades speed for a truer annual average.
Sometimes the timing is not yours to choose: a purchase contract sets the test date, not the furnace. Real estate radon testing happens whenever the closing calendar says, and the EPA's decision points apply to that result the same as in January. When one report leaves the question open, a professional radon test in Lincoln under closed-house conditions replaces an argument with a measurement.
When Every Season Says the Same Thing
Plenty of Lincoln houses skip the ambiguity and read above the action level in July and January alike. Then the question is not which month to believe but how soon to act. The case for fixing a high radon level in a Lincoln home does not depend on which month produced the number — the fan in an active system runs year-round and holds the level down through both halves of the cycle.
Installation is a year-round job too. A sub-slab depressurization system goes in the same way in February as in June, and the verification test afterward reads the system's performance in whatever season it runs. The seasons complicate measurement — not the fix.
More from the blog
- Short-Term vs Long-Term Radon Tests in Lincoln
- Closed-House Conditions: What They Mean for a Lincoln Radon Test
- Buying a Lincoln Home That Already Has a Radon System
Quick Answers
Is a summer radon test still valid?
Yes. A properly run test measures what was in the air during its window, and a summer result at or above 4 pCi/L is as actionable as a winter one — the EPA's action level does not move with the calendar. What deserves double-checking is a low or borderline summer number, which may not represent the heating season.
How much higher will a winter reading be?
There is no fixed conversion factor. The swing depends on the house, the weather, and how the home was used that week, so a July number cannot be converted to a January number on paper. The only ways to know are a second test under heating-season conditions or a long-term test that includes them.
Does air conditioning interfere with a radon test?
Central air is fine — it recirculates indoor air rather than pulling in outside air. What matters is keeping closed-house conditions: windows shut, exterior doors used only for normal coming and going, no whole-house or window fans running. An air-conditioned home in July often meets those conditions more easily than an open-windowed one in May.