Why season affects a radon test result
Radon testing measures the radon level in a home during a specific window, under specific conditions, so the conditions during the test matter as much as the test itself. A short-term test performed with windows occasionally opened, doors propped for showings, or unusually mild weather may not reflect how the home behaves once it is sealed up for winter. That is one reason a result from an early fall test can differ from a result taken during the coldest part of the year, even in the same house.
What closed-house conditions mean
Closed-house conditions generally mean windows and exterior doors remain closed except for normal entering and exiting, and the home's heating and cooling system runs as it normally would, typically starting at least 12 hours before the test begins and continuing through the test period. Park City's winters make this easy to achieve without extra effort, since most homes are already sealed up against the cold. During milder months, homeowners and agents sometimes need to deliberately keep the house closed up for the test window, which can be harder to coordinate around showings, guests, or nice weather.
Why many Park City professionals prefer winter testing
Because winter closed-house conditions are closer to a worst-case scenario for radon accumulation, many radon professionals view heating-season testing as producing a more representative short-term result. That is part of why winter and early-spring test requests are common in Park City, both for general homeowner planning and for real estate transactions that happen to fall during ski season. A test performed in July with windows open on a warm evening is not necessarily wrong, but it may understate what the home experiences for the several colder months each year.
Second homes, vacation rentals, and winter access
Second homes and vacation rentals add a practical wrinkle: winter is also peak occupancy season for many Park City properties, which can make scheduling a quiet, undisturbed 48-hour test window more difficult around guest turnover. Coordinating a test date during a gap between reservations, or during an owner's own stay, is often the most practical approach. Property managers requesting testing on behalf of an owner should have access details and the rental calendar ready when reaching out.
Testing outside of winter
A home does not have to be tested in winter. Closed-house conditions can be maintained at any time of year with some planning, and long-term test devices, left in place for 90 days or more, can capture a broader seasonal pattern that includes both summer and winter conditions. The choice between a quick winter short-term test and a longer multi-season test often comes down to the deadline: real estate transactions usually need a fast result, while a homeowner without a deadline may prefer the fuller picture a long-term test provides.
Next steps
For general testing information and choosing between short-term and long-term tests, see the radon testing page. For a transaction with a closing date to plan around, see the real estate radon testing page. If a winter test comes back elevated, the radon mitigation guide and mitigation cost guide cover the next steps and pricing factors.
Winter radon testing FAQs
- Is winter really the best time to test for radon in Park City?
- Many radon professionals consider winter, closed-house conditions favorable for short-term testing because homes are sealed up for heating season, which tends to be closer to worst-case conditions than a mild shoulder-season week.
- Can radon levels really change between summer and winter?
- Yes, radon levels can vary with weather, ventilation habits, and how tightly a home is sealed, which is why the same home can produce different short-term results depending on when and how it is tested.
- What counts as closed-house conditions for a test?
- Generally, windows and exterior doors staying closed except for normal entry and exit, and the home's heating and cooling system operating as usual, for at least 12 hours before and during the test period.
- Do I have to test in winter, or can I test any time?
- A home can be tested at any time of year if closed-house conditions are maintained during the test. Winter simply makes those conditions easier to achieve without extra effort since the home is already sealed up for heating season.