Radon Fan: How It Works, Sizing, Cost, and When to Replace It
A radon fan pulls about 60 watts from the wall. It runs 24 hours a day. And it’s the one part of your mitigation system that will eventually wear out.
Most Ontario homeowners never think about the fan until it goes quiet. By then, the radon has already crept back up.
This guide covers what a radon fan actually does, how to pick the right size, where it goes on your home, what it costs to replace, and the small handful of fan jobs a handy homeowner can do alone.
The short version:
- A radon fan creates suction under your slab and vents soil gas above the roof
- Fans last 10 to 15 years. Replacement parts run $200 to $500.
- Exterior placement (side wall or roof) is the North American default; Health Canada also accepts interior placement when every pipe joint is airtight
- A failing fan shows up first on the manometer (the U-tube pressure gauge near the pipe)
- DIY fan swaps on an existing system are doable. Designing a system from scratch is not.
- Fantech and RadonAway are the two brands most Ontario installers use
What a radon fan actually does
A radon mitigation system has three parts: a hole drilled through your slab, a PVC pipe sealed into that hole, and a fan pulling air through the pipe. The fan is the only moving part.
It works by creating negative pressure under the slab. Soil gas (radon plus moisture plus whatever else) wants to flow from high pressure to low pressure. The fan makes the area under your basement floor lower-pressure than the soil outside. Radon flows up the pipe instead of into your living room.
The technique is called active sub-slab depressurization. The EPA and Health Canada have recommended it for over 30 years.
The fan itself is a sealed, inline unit. Air enters one side, exits the other.
There’s no filter to change. No oil to add. It just runs.
Sizing: which fan goes on which house
A radon fan isn’t one-size-fits-all. The wrong fan either fails to pull enough air (radon stays high) or pulls too much (you waste power and may overdraft your basement).
Two specs matter:
- CFM (cubic feet per minute): how much air the fan can move
- Static pressure: how hard it can pull against resistance
A small Ontario home with a clean full basement and one suction point needs a small fan. A 3,500 sq ft home with a crawl space and two suction points needs a bigger one.
| Home size | Foundation | Typical fan | Static pressure draw |
|---|---|---|---|
| Under 2,000 sq ft | Full basement, single suction | RadonAway RP140 or Fantech HP190 | Low |
| 2,000 to 3,500 sq ft | Full basement, single suction | RadonAway RP145 or Fantech HP220 | Medium |
| Over 3,500 sq ft | Multi-foundation or crawl space | RadonAway GP501 or Fantech HP2190 | High |
| Tight soil (clay) | Any | One model up from the chart | Very high |
The installer should run a diagnostic during the site visit. They drill a small test hole, measure the pressure under your slab with a real gauge, and pick the fan that matches.
A “guess and check” install is a yellow flag. The fan on your system should be matched to your house, not picked off a shelf.
Indoor vs exterior fan placement
Where the fan sits on your home isn’t a style choice. There’s a safety rule behind it.
The North American mitigation standard puts the fan outside the home, with the exhaust above the roofline.
If the fan sits in the basement, the positive-pressure pipe runs through your living space. A small leak there pumps radon back into the house.
If the fan sits outside (mounted on the wall above the eaves, or on the roof), the only positive-pressure pipe is outside the house. A leak just vents soil gas to the air, which is harmless.
The three common Ontario placements:
- Side wall, above eave height. Most common. Quiet, easy to service, no roof penetration.
- Roof-mounted. Used when the pipe routes up through finished living space. Looks like a furnace stack.
- Attic. Acceptable if the attic is sealed from the living space, but it’s a compromise. Most C-NRPP CRMT installers avoid it.
Basement-mounted fans are accepted by Health Canada but require extra care. Every pipe joint, the fan housing, and the seal where the pipe enters the slab must be airtight. A leak on the fan’s pressurized side pumps radon back into your living space. Most Ontario installers prefer exterior placement because the safety margin is built into the geometry rather than the installer’s caulk lines. Garage-mounted fans are not recommended: the pipe passing through unconditioned space causes condensation and freezing problems in Ontario winters.
Cost: install, replacement, and parts
A full new system in Ontario runs $2,800 to $3,800 including the fan. Replacement of just the fan on an existing system is much cheaper.
Replacing a fan on an existing system
| Part of the job | Typical cost |
|---|---|
| Fan unit (RadonAway or Fantech) | $200 to $500 |
| Rubber couplings (2) | $20 to $40 |
| Sealant and clamps | $15 |
| Labour (1 hour, if hiring) | $150 to $300 |
| Post-replacement re-test | $99 to $299 |
Total: $300 to $1,000 depending on whether you DIY the swap and which test you run afterward.
Most homeowners pay between $400 and $700 for a professional fan replacement with no re-test, or $700 to $1,000 with a re-test included.
Why some quotes are higher
A few patterns to watch:
- “We have to redesign the system”: rare. A working system that ran for 12 years just needs a new fan. The pipe and pit are still fine.
- “You need a bigger fan now”: maybe. If your post-mitigation reading was borderline (just under 200 Bq/m³), an upsize makes sense. Otherwise it’s a sales add-on.
- Charging for a full new system to replace a $400 fan: this happens. Get a second opinion.
Signs your radon fan is failing
You won’t smell it. You won’t hear an alarm. A failing fan gives one quiet, specific signal: the manometer changes.
A manometer is the small U-shaped tube of red liquid mounted on the pipe near the wall. When the fan runs at full power, the two sides of the liquid are offset by about 1 to 2 inches. When the fan fails, the two sides equalize.
The four warning signs, in the order they usually show up:
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Manometer reading drops. From 1.5” to 0.5” of pressure difference, for example. The fan is weakening.
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Manometer evens out completely. The fan has stopped pulling. The system is doing nothing.
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The fan gets louder. A grinding or buzzing sound means the motor bearings are going. Replace soon.
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A retest reads higher. Your home tested at 75 Bq/m³ after install. Three years later it reads 250 Bq/m³. The fan stopped working at some point in between.
The manometer is your early warning system. Check it once a month. It takes two seconds.
Some newer monitoring fans (Fantech RN series, RadonAway GX series) have a built-in alarm or app alert. Worth the small extra cost if you forget to check the gauge.
DIY radon fan replacement: when it makes sense
This is one of the few radon jobs a handy Ontario homeowner can do alone. The full install is a different story (see our Ontario mitigation cost guide for the bigger picture). But a fan swap on an existing, working system is straightforward.
What you need
- Replacement fan (same brand, same pipe size, same or higher CFM)
- Two new rubber couplings sized for your pipe (usually 3” or 4”)
- Stainless steel hose clamps (4 of them)
- Outdoor-rated electrical box if the existing one is cracked
- Ladder, screwdriver, hose clamp tool
Total parts: about $250 to $500. Total time: 30 to 60 minutes if you’ve done basic plumbing work.
The eight-step swap
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Cut the power. Flip the breaker that feeds the fan. Use a voltage tester to confirm.
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Loosen the rubber couplings. One above the fan, one below. Use a screwdriver on the hose clamps.
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Disconnect the wiring. Open the outdoor electrical box, cap the wires, label which is which.
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Pull the old fan off the pipe. It should slide straight out once both couplings are loose.
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Slide the new fan into position. Match the arrow on the housing (it shows airflow direction, must point up).
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Re-clamp the couplings. Tight enough to seal, not so tight you crush the rubber.
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Reconnect the wiring. Same wire to same terminal. Close the box.
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Power back on. Watch the manometer. Reading should jump back to its old offset within 30 seconds.
When NOT to DIY
- You don’t have an existing working system. Designing one from scratch needs a C-NRPP CRMT certified installer.
- The roof or wall mount is damaged. Sealing failures are how radon gets back in.
- Your system has electrical issues, not just fan issues. Hire an electrician.
- You’re filing a Tarion warranty claim. Tarion requires certified work on the entire warranty path.
- You’re not comfortable working above eave height on a ladder. The job’s not worth a fall.
Hiring out a fan swap costs $400 to $700. DIY saves you $200 to $400. For most people who already own a basic toolkit, it’s worth doing alone.
Common Ontario fan brands and what to expect
Two brands cover roughly 90 percent of Ontario radon installs.
RadonAway
The most common brand. RP145 and RP265 are the two models you’ll see on most GTA and Southern Ontario homes. Reliable, widely stocked, easy to find replacement parts. 5-year manufacturer warranty.
Fantech
The other major brand. HP190 and HP220 are the residential workhorses. Slightly higher static pressure tolerance than equivalent RadonAway models, which matters for clay soils. 5-year warranty.
Festa and others
Specialty brands appear on commercial installs and larger custom homes. If your existing fan is a brand you can’t find, swap to a sized-up RadonAway or Fantech equivalent.
A few things to confirm before buying:
- Pipe size match. 3-inch vs 4-inch fans aren’t interchangeable.
- Outdoor rating. Indoor-rated fans fail fast in Ontario winters.
- UL or CSA listing. Required by Canadian electrical code.
The Government of Canada’s plain-English radon overview is a good starting point if you want the policy and health framing behind any of this. The C-NRPP public directory
Where Breathe Radon Free fits
We’re an Ontario-based testing service, owner-led, based in Guelph and serving the Greater Toronto Area plus surrounding Southern Ontario.
For fan replacement specifically:
- If your manometer dropped and you’d rather have someone else do the swap, we can refer you to a local C-NRPP CRMT installer.
- If you just need to confirm the system is still working, a $99 short-term test gives you a clear yes or no.
- If you bought a home with an older mitigation system and aren’t sure what shape it’s in, the test is the cheapest first step.
Our published pricing:
- Residential test: $99 flat. 3 to 7 days, written report.
- Real estate test: $399. Faster turnaround for closing timelines.
- Long-term test: $299. 91-day alpha track for ongoing residential.
- Mitigation install: $2,800 to $3,800. Full system with 5-year workmanship warranty.
- Tarion claim help: free for test customers.
Book a $99 test to confirm your system still works. Or see full service details.
Frequently asked questions
How long do radon fans actually last in Ontario homes?
Most fans run 10 to 15 years before failing. Ontario winters are harder on outdoor-mounted fans than mild climates, so plan toward the lower end of that range. Indoor (attic or basement) fans last a bit longer because they’re climate-controlled.
The manometer is your real timer. When the reading drops, the clock has run out.
Can I just replace the fan with a bigger one for better results?
Sometimes, yes. If your post-mitigation test came back borderline (between 100 and 200 Bq/m³), bumping up one model size can drop it further. The risk is overdrafting your basement, which can pull combustion gases backward through a furnace or fireplace. Get a diagnostic first, or have a C-NRPP CRMT installer confirm the upsize is safe.
Will the warranty cover a failed fan?
The fan itself usually has a 5-year manufacturer warranty (RadonAway, Fantech, and most major brands). After year 5, you’re paying for parts. The labour warranty from the installer is separate, usually 5 years too. For new builds in Ontario, the Tarion warranty covers the radon mitigation system for 7 years (mitigation done under the warranty is a different path).
Do radon fans make noise?
A properly installed exterior fan is quieter than a dishwasher. You’ll hear a soft hum if you stand next to the pipe outside. Indoor-mounted fans can rattle through ductwork or HVAC chases if they aren’t isolated with rubber couplings. A loud or buzzing fan usually means it’s near the end of its life.
How much electricity does a radon fan use?
About 60 watts, continuously. That’s roughly $5 to $10 a month on an Ontario hydro bill at current rates. Over a 12-year fan life, that’s about $1,000 in electricity.
A small price for cutting your indoor radon by 90 percent. Some newer ECM-motor fans (variable speed) cut that to about 30 watts continuous, half the running cost.
What’s the Canadian guideline for indoor radon levels?
Health Canada’s action level is 200 Bq/m³.
Book a $99 radon test to confirm your fan still works
Authored by the Breathe Radon Free Team. Every claim is backed by a primary source. Full bibliography at /sources.
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