Quick answer
If your radon system's fan has died, buy the same model or one whose published fan curve covers the suction your manometer showed, and for most 4 in systems that is the RadonAway RP145C, rated 4.4 stars across 1,403 Amazon ratings. Its listing says it is the standard RP145 under a different label, with 4.5 in inlet and outlet collars that join 4 in schedule 40 PVC through rubber couplings. Compare fans by airflow at a stated static pressure, not peak CFM. For a new system, EPA points you to your state radon program for qualified professionals, and advises fixing a home that tests at 4 pCi/L or more.
Buyer's Guide
What to know before you buy.
What a Radon Fan Does, and Why It Is Only One Part of the System
A radon fan does not filter or clean anything. In a sub-slab depressurization system, it pulls soil gas from a hole cut through the slab, up a sealed pipe and out above the roof, so the soil under your floor sits at slightly lower pressure than the air in your basement. That small suction is what keeps radon from seeping in. EPA describes soil suction the same way: radon is drawn from below the house and vented through pipe to the air above it, where it quickly dilutes. The fan only works as part of that whole. Slab cracks, sump pits and floor drains have to be sealed, or the fan pulls basement air instead of soil gas. RadonAway's own listing says as much. A bigger fan on a leaky slab mostly costs you power and heated air.
Sizing: Airflow at Your Suction, Not the Biggest CFM Number
Every radon fan trades airflow for suction. The Fantech Rn2 listing shows how steep that trade is: 123 CFM at 0.50 in of static pressure, but only 20 CFM at 1.75 in. Which point matters depends on what is under your slab. Loose gravel lets air move easily, so the system runs at low suction and needs flow. Tight clay or wet soil resists flow, so the fan has to hold high suction instead. On an existing system, the U-tube manometer on the pipe is your sizing data. Write down its reading before the old fan comes out, then choose a fan whose published curve still moves air at that number. A CFM figure with no pressure attached, like the 260 CFM on several listings here, most likely describes a fan blowing into open air, which a sub-slab fan never does.
Replacing a Failed Fan vs Designing a New System
A like-for-like swap is the job most buyers of a radon fan are doing. If the system tested low before the fan failed, the pipe, seals and suction point are already proven, and you are replacing a motor. Cut the power, loosen the couplings, fit the same model or one whose curve covers your manometer reading, and retest the house afterward. A new system is a different job. It starts with a test result, then checks under the slab to see how far suction reaches, then the suction point, sealing and pipe route. EPA's route for that work is your state radon program, which can help you find qualified professionals. States that receive EPA radon grants list providers credentialed by the state or by one of two national programs, the NRPP and the NRSB, and some states set requirements of their own.
Where the Fan Goes: Attic, Garage or Outside Wall, Never the Basement
Mount the fan outside the living space: in the attic, in an attached garage, or on an exterior wall. Everything after the fan is under positive pressure, so a cracked joint on that side pushes radon-laden air out wherever it leaks. With the fan outside the living space, that leak happens where nobody breathes it. The exhaust then has to rise above the roof. EPA explains that it disallowed ground-level discharge because the gas can be drawn back into the house and children could be exposed, and that radon falls to near background levels 3 to 4 ft from the discharge point. Outdoor mounting needs a fan stated for it, such as the IP67 MIDCVFRUN kit, and a weatherproof electrical connection. Hardwiring and any outdoor disconnect follow local electrical code, which is an electrician's call.
Checking It Works: The U-Tube Manometer, Noise and Power
The U-tube manometer on the pipe is your running check. With the fan on, the liquid sits higher on one side, and the difference, in inches of water column, is the suction. If both sides are level, the fan has stopped or the pipe has come apart, and from the living room you would not hear the difference. EPA advises looking at your system's warning device regularly and retesting the home at least every two years. It also notes that fans may last five years or more, with maker warranties that tend not to exceed five. Power is the running cost to plan for. A fan runs 8,760 hours a year, so a 70-watt draw, the ceiling on Festa's listing, comes to about 613 kWh a year. Noise varies more than people expect: listings here state anything from 32 dB to 60 dB.
Who Should Not Buy a Radon Fan Yet
Do not buy a fan before you have a test result. EPA's advice is to fix a home when radon is 4 pCi/L or more and to consider fixing between 2 and 4 pCi/L, so the number decides whether you need a system at all. By EPA's estimate, radon is the number one cause of lung cancer among non-smokers, which is why a test, not a hunch, should drive this purchase. A fan on its own does nothing in a house with no suction point or pipe; that home needs a designed system. A crawl space with a dirt floor needs a sealed membrane first, with suction drawn from under it. A dehumidifier or air purifier does not stop soil gas from entering, so neither is a radon fix. And if a retest stays high after a fan swap, call a qualified mitigator rather than buying a bigger fan.
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