Do you need a radon mitigation system?
You need a radon mitigation system once a long-term reading on the lowest level you use averages 4 pCi/L or higher, the EPA's action level for fixing a home. Between 2 and 4 pCi/L, the agency says a radon system is worth considering. Below 2 pCi/L, most homes don't need one.
Maybe a pre-sale test kit came back at 5 pCi/L and the seller is already arguing about it, or a neighbor mentioned their own number and now yours feels like a guess. Either way, one reading rarely settles the question on its own. This post walks through what a radon mitigation system actually does, the number that decides whether you need one, and how to confirm it worked once it's in.
Key Takeaways
- The EPA's action level for installing a radon system is 4 pCi/L; it says to consider one between 2 and 4 pCi/L.
- A radon mitigation system vents soil gas from under the foundation before it reaches the rooms people use.
- A single short-term test can miss the picture. Radon needs months of data to read reliably, unlike CO2 or PM2.5.
- A licensed mitigation contractor installs and quotes the system. A monitor's job is the reading before and after, not the install.
- A retest after installation is the only way to confirm the number actually dropped.
What a radon mitigation system does
A radon mitigation system is almost always sub-slab depressurization: a contractor drills a hole through the foundation slab or sump pit, runs a vent pipe up through the house to above the roofline, and fits a fan partway up that pulls soil gas out from under the house and releases it outside. The point is to intercept the gas before it ever gets into the air people breathe, not to filter it once it's already indoors.
A second, smaller category covers simpler fixes: sealing major cracks and openings in a foundation, or adding ventilation to a crawlspace. The EPA's consumer guide to radon reduction notes that sealing alone rarely lowers radon enough on its own, which is why most contractors pair it with a vent system rather than relying on it by itself.
The number that decides: EPA's action levels
At 4 pCi/L or above, the EPA recommends fixing the home. From 2 to 4 pCi/L, it says a fix is worth considering, especially with small children in the house or a reading that's been climbing. Below 2 pCi/L, the agency doesn't recommend a system at all.
For reference, the World Health Organization sets a lower reference level of about 2.7 pCi/L (100 becquerels per cubic meter) and recommends acting closer to that number where it's practical. Neither agency treats radon as something to eliminate entirely: it comes up from the ground almost everywhere. The question is how much is in the house, not whether any is.
Why one reading isn't enough to decide
Radon moves with the seasons. A closed house with the heat running pulls more soil gas in through the lowest level than the same house with the windows open, so a test run in July can understate what the same room sees in January. How radon levels change by season covers why a single number is a snapshot, not a trend.
A short-term kit, run for 2 to 90 days, answers fast: good for a home sale with a closing date, less reliable for deciding whether to spend money on a system. A long-term test or a continuous monitor left running for a full season or a year gives a steadier average to act on. How a radon test kit works walks through both kinds and where to place one.
Getting a radon system installed
Once a reading supports it, the next call is to a licensed radon mitigation contractor, not a general handyman. A contractor assesses the foundation type (slab, basement, crawlspace), figures out where to drill and route the vent pipe, and installs the fan and alarm that flags if it ever stops running. Installation typically takes a day.
A radon system is specific to the job: a contractor quotes it after seeing the house, since foundation type and vent routing both change the work. That conversation, and the system itself, sits with the contractor. A monitor's role is the reading that tells you whether the job is worth doing, and later, whether it worked.
Confirming the system worked
A radon system isn't done the day the fan turns on. The EPA recommends a retest within 30 days of installation to confirm the number actually dropped below 4 pCi/L, since a badly sealed slab or an undersized fan can leave a system underperforming even after it's running.
Keep measuring after that first retest too. Radon still shifts with the seasons even with a system in place, and a fan that fails or an alarm no one notices can let the number drift back up months later. Tracking the reading over time, rather than checking it once and moving on, is what shows the system is still working the next winter, and the one after that.
Where to measure, before and after
Test on the lowest level you actually use, not wherever is convenient. A finished basement used daily qualifies; an unfinished one visited twice a year doesn't, and the first floor is the better stand-in for the air a household breathes. Keep the monitor away from drafts, exterior doors, and windows, all of which can pull in outside air and push a reading down for reasons that have nothing to do with the house.
Use the same spot before and after installation. Moving the monitor between the baseline reading and the follow-up makes the comparison meaningless, since a reading from a different room settles a different question.
A Measured Air kit reports radon alongside PM2.5, CO2, VOCs and humidity, and keeps every reading in history, so the baseline from before installation sits next to the retest after, instead of two numbers in two different places.
FAQ
Do I need a radon mitigation system if my reading is between 2 and 4 pCi/L? The EPA doesn't require one in that range but says a fix is worth considering, especially with a rising trend or young children in the house. Most homeowners base the call on a longer average rather than a single test in that range.
How do I know if a radon mitigation system is working? A retest within 30 days of installation is the only way to confirm it. The number should sit below 4 pCi/L, and ongoing readings over the following seasons confirm the fan and seal are still doing the job.
Can I test for radon myself before calling a contractor? Yes. A short-term kit or a continuous monitor both report in pCi/L without a contractor visit. What the number says next, whether to call a contractor, is the only part that needs one.
Does every home need a radon system? No. Below 2 pCi/L, the EPA doesn't recommend any action, and the national average indoor reading is about 1.3 pCi/L. Radon systems are for homes whose reading actually supports one.
How long does a radon system take to install? Most sub-slab depressurization systems install in a single day, though the exact routing depends on the foundation. A contractor who has seen the house gives the real timeline.
Will sealing cracks in my foundation fix a high radon reading? Rarely on its own. The EPA notes that sealing alone usually isn't enough to bring a high reading down, which is why most fixes pair it with a vent and fan system rather than relying on sealing by itself.
The bottom line
A radon mitigation system earns its place once a reading averages 4 pCi/L or higher, and it's worth a look between 2 and 4 pCi/L. Getting there takes more than one test: radon shifts with the seasons, so the lowest level you actually use, measured over time, is what the decision should rest on. A licensed contractor installs the system itself; a monitor's job is the number before, the retest after, and the readings that confirm it keeps working.
Order a kit sized to your home, start a radon baseline on the level you use most, and see every reading from the homeowners page next to the outdoor air at your address.