If you just bought your first home (or are about to), radon is one of the less obvious items on the homeownership checklist — easy to overlook because it’s invisible and rarely comes up in casual conversation. Here’s a practical starting point.
Radon is worth understanding once rather than researching repeatedly, because the whole decision reduces to three questions in order: has this house been measured, what did the measurement say, and does that number call for action. Everything else is detail underneath those three.
- Check whether radon testing was already done as part of your home purchase.
- A basic DIY test kit is a reasonable first step if no recent test exists.
- Below 4 pCi/L: no immediate action required; at or above: mitigation is recommended.
- Retest 30 days after any mitigation, then annually going forward.
Step 1: Find Out If Testing Was Already Done
Check your closing documents and inspection report — many real estate transactions include a radon test as part of the inspection contingency. If a test was done, get the actual pCi/L number and date, not just a pass/fail summary.
When you retrieve a prior result, get the number and the date, and also get the conditions. A short-term test is only valid if the house was held under closed-house conditions, meaning windows and exterior doors kept shut apart from normal entry and exit, for twelve hours before the measurement began and throughout it. Vacant houses during a sale are frequently aired out for showings, so a low result from a marketing period is weaker evidence than the same number would be otherwise.
Season matters for the same reason. Indoor levels are usually highest in cold weather, because the stack effect is strongest then. Warm indoor air rises and escapes at the upper part of a building, leaving the lowest level slightly depressurized relative to the soil beneath it, and that pressure difference is what draws soil gas in through slab cracks, service penetrations and sump openings. A summer result from an open house is the least conservative measurement you can hold, and it is the one most likely to be presented as reassurance.
If no test exists, or it’s more than a couple of years old, plan to test soon after move-in — radon can be present regardless of whether a prior test was done or what it showed at the time.
Step 2: Buy a Test Kit or Hire a Professional
A short-term DIY test kit ($15-$30) from a hardware store is a reasonable, low-cost starting point for a first-time homeowner. Follow the closed-house instructions carefully, and send it to the specified lab promptly after the test period ends.
Placement is the part of a DIY test most often done wrong. The detector belongs in the lowest level of the home you occupy or reasonably could occupy, which means a finished basement counts even if you rarely use it [1]. Put it in the breathing zone, roughly two to six feet above the floor, away from exterior walls, away from drafts, heat and direct sun, and away from areas of high humidity such as a bathroom or directly beside a laundry, since charcoal devices in particular respond to moisture. Leave it undisturbed for the full period the instructions specify.
Post the kit to the laboratory promptly once the deployment ends, because the measurement is time sensitive and a canister sitting in a car for a week degrades the result. Before buying, check whether your state radon programme distributes free or discounted kits, as many do, with availability often concentrated around National Radon Action Month in January [2]. Where an initial short-term result lands close to the action level, the sensible follow-up is a long-term detector left in place for months, which reports an annual average rather than a snapshot.
If you want a more authoritative result — especially if you’re already suspicious based on your home’s location or construction — a certified professional test is a modest additional cost and removes any doubt about proper placement or handling.
Step 3: Know What to Do With the Result
Below 4 pCi/L: no immediate action needed, though the EPA notes any level carries some risk and mitigation can be considered even below the action level if you want to minimize exposure further.
It helps to know what the standard system actually is, since the phrase sub-slab depressurization describes something quite simple. A pipe is sealed into a hole cut through the slab, a continuously running fan on that pipe draws air from the gravel or soil beneath the floor, and the extracted gas is discharged above the roofline away from windows. This holds the space under the slab at slightly lower pressure than the house above it, so soil gas travels up the pipe rather than through the floor. It does not filter the air inside your home and is not related to an air purifier.
Two details are worth carrying with you into any conversation about installation. The fan must sit outside the conditioned space, in an attic, an unconditioned garage or outdoors, because the pipe on the discharge side of the fan is under positive pressure and a leak there inside the house would push concentrated soil gas indoors. And the small U-shaped manometer on the pipe shows only that a pressure difference exists across the fan. It confirms the fan is running. It is not a radon measurement, which is why a retest after installation and periodically afterwards is the only real confirmation the system is working.
At or above 4 pCi/L: the EPA recommends mitigation. That usually means an active sub-slab depressurization system installed by a certified mitigator, which typically runs $800-$2,500. Retest 30 days after mitigation and annually afterward.
Ordinary Things That Change Your Reading
Once you know the mechanism, several everyday events stop being mysterious. Radon enters because the lowest level of the house is slightly depressurized relative to the soil, so anything that increases that imbalance tends to increase entry. A powerful kitchen range hood, a bathroom extractor, a clothes dryer and an open flue all remove indoor air, and the replacement air is drawn from wherever the building leaks, including from below the slab. This is a real effect and not a reason to avoid using extractor fans, but it explains why readings move.
Weather does the same. Wind and falling barometric pressure change the pressure relationship between the soil and the house, which is why a stormy week can produce a noticeably different reading than a calm one in the same building. It is also why a single hourly figure from a continuously displaying monitor is not a result. Those devices are useful for seeing patterns and for keeping an eye on a mitigated house, and the number to read is the multi-week average rather than whatever is on the screen at a given moment.
One further item is easy to miss in a first house, which is that a private well is a separate pathway with a separate remedy. Radon dissolved in groundwater is released into indoor air when water is agitated, in showers, dishwashers and washing machines. A sub-slab system does nothing about this, because it addresses soil gas rather than water. If your water comes from a private well and your air result is elevated, testing the water is a distinct test worth asking about, as the treatments for it are different equipment entirely.
FAQ
Is radon testing something I need to do right away as a new homeowner?
It’s not an emergency, but it’s worth prioritizing in your first few months, especially if no recent test exists in your closing documents.
Where exactly should I place a test kit?
In the lowest level you occupy or reasonably could, two to six feet above the floor, away from exterior walls, drafts, direct sun, heat sources and humid areas such as bathrooms or laundries. Leave it undisturbed for the whole period, then post it to the lab promptly.
Does a radon system clean the air in my house?
No. Sub-slab depressurization keeps the space beneath the floor at slightly lower pressure than the rooms above, so soil gas travels up a pipe and discharges above the roofline instead of entering. It is not a filter and is unrelated to an air purifier.
Why does my reading change so much day to day?
Because entry depends on the pressure difference between the soil and the house, and that shifts with weather, wind and anything that removes indoor air such as range hoods, bathroom fans and dryers. This is why the average over a longer period, rather than any single reading, is the meaningful figure.
What if I can’t afford mitigation right now?
A short-term DIY kit is inexpensive and low-risk to run first. If it confirms an elevated level, you can plan and budget for mitigation, potentially in phases, rather than treating it as an immediate financial emergency.
This guide is a general starting point. Always follow the specific instructions provided with your chosen test device or professional service.
References
- Radon in Homes, Schools and Buildings. U.S. Environmental Protection Agency
- Find a Radon Test Kit or Measurement and Mitigation Professional. U.S. Environmental Protection Agency
These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure, or prevent any disease. Content is for informational purposes only and is not medical advice; consult a qualified healthcare provider before starting any supplement. As an Amazon Associate we earn from qualifying purchases.
