Why Testing Comes First
Radon has no color, smell, or taste, so a test result is the only way to know whether a Bismarck-area home has an elevated level. This applies regardless of a home's age, size, or foundation type, and regardless of whether a neighboring home has already tested high or low — soil gas pathways, foundation condition, and how a specific house is built can all vary enough from one address to the next that a neighbor's result is not a substitute for testing your own property.
Short-Term Versus Long-Term Testing
A short-term test typically runs from 2 to 90 days and is the common choice for real estate transactions and homeowners who want a faster answer. Devices used for short-term testing include charcoal canisters and electret ion chambers, which are sent to a lab or read by a professional after the test period ends. A long-term test runs for more than 90 days and gives a better picture of a home's average radon level across different seasons and weather conditions, since radon levels can shift with temperature, wind, and how tightly a home is sealed at different times of year. Homeowners who are not on a real estate deadline and want the most representative picture of their year-round exposure sometimes choose a long-term test, or follow up an elevated short-term result with a longer test before deciding on mitigation.
Continuous Radon Monitors
Continuous radon monitors are digital devices that record hour-by-hour or day-by-day readings rather than producing a single average number. Radon professionals use them for diagnostic work and post-mitigation verification, and more homeowners are also using them for ongoing awareness after an initial test. Because they show how levels move over time, continuous monitors can help identify whether a spike is tied to a specific weather pattern, a furnace or HVAC cycle, or a door left open, information a single short-term average can't provide on its own.
Closed-House Conditions And Winter Timing
Standard testing protocol calls for closed-house conditions: windows and exterior doors kept shut except for normal entry and exit, generally starting roughly half a day ahead of placing the device and staying in effect for the entire test period. Because North Dakota homes are already sealed up tightly for months during the heating season, many radon professionals recommend testing in the colder months, when closed-house conditions reflect how the home behaves for most of the year rather than an unusually ventilated week. That said, a properly conducted test following closed-house protocol can be performed at any time of year, which matters for real estate transactions that don't line up with winter.
Testing During A Real Estate Transaction
Buyers and sellers in the Bismarck-Mandan area frequently order a radon test during the inspection period of a home sale, on a much tighter timeline than a routine homeowner test. Lender requirements or the terms of a purchase agreement sometimes call for a qualified radon measurement professional to place and retrieve the device, with tamper-evident placement so the result holds up through closing. Placement still follows the same general rules — lowest livable level, away from drafts and exterior doors — but scheduling has to work backward from the closing date.
Reading Your Result
Results are reported in picocuries per liter (pCi/L). The EPA recommends fixing a home at a result of 4 pCi/L or higher, and considering a fix when a result falls between 2 and 4 pCi/L. A borderline result near the action level sometimes leads to a follow-up long-term test before deciding on mitigation, since short-term tests capture a snapshot rather than a full-year average. If a result comes back at or above 4 pCi/L, the next step is typically mitigation system installation, and the cost guide covers what to expect once you're ready for a quote. New home buyers should also check whether radon-resistant construction features were included, since even those homes should be tested after move-in.
Factors That Can Affect A Test's Accuracy
A handful of conditions can throw off a test result if they aren't controlled for. Opening exterior doors or windows during the test period, running a whole-house fan or fireplace, or unusually strong wind and barometric pressure swings during a short test window can all shift a reading away from what the home's typical level actually is. This is part of why closed-house protocol specifies keeping doors and windows shut for the duration, and why professionals placing a device for a real estate transaction often use tamper-evident seals — not because homeowners are assumed to be doing anything wrong, but because a disturbed test has to be thrown out and redone, which can be costly on a closing timeline.
Retesting After A Remodel Or HVAC Change
Radon levels are not fixed for the life of a house. A finished basement, a new furnace or ventilation system, added insulation, or foundation repair work can all change how air moves through a home and, in turn, how radon behaves inside it. Homeowners who test once, get a low result, and then make a significant change to the home's envelope or mechanical systems a few years later are generally well served by testing again rather than assuming the original result still applies.
Radon Testing Questions
- How long does a radon test take?
- A short-term test typically runs for 2 to 90 days, most often 2 to 7 days for a real estate transaction, while a long-term test runs for more than 90 days to capture a broader seasonal average.
- Can I test my own home, or do I need a professional?
- Homeowners can place a short-term test kit themselves for general information, but real estate transactions, lender requirements, and some closing timelines often call for a qualified radon measurement professional to place and read the device.
- Where should the test device be placed?
- Devices are generally placed in the lowest livable level of the home, away from drafts, exterior doors, windows, and sources of heat or moisture, and left undisturbed for the full test period.
- What do I do if my result is above 4 pCi/L?
- A result at or above 4 pCi/L is the EPA's recommended action level, and the next step is typically to look at mitigation system installation options for the specific foundation type.
- Does a low result mean I never need to test again?
- Not necessarily. Radon levels can change after a remodel, foundation repair, or changes to a home's ventilation, so retesting every few years or after major changes is a reasonable practice.