Why Radon Systems Freeze in Canadian Winters — and How Canadian-Style Systems Prevent It

Every winter, radon systems across Canada quietly stop working — fan still humming, manometer flat — because ice has closed the pipe. It's predictable physics, and it's the reason Canadian mitigation practice deliberately differs from what American websites tell you. If you've read US advice saying the fan must live in the attic and vent above the roof, this page explains why Canadian standards say otherwise — and how to keep your system running at −30.

Why Systems Freeze

The air a radon fan pulls from under your slab is moist. Health Canada's Radon Reduction Guide for Canadians puts it plainly: in many Canadian climates, a fan and pipe located outside the living space (garage or attic) will cool during the colder months, “leading to condensation and possibly ice, which can damage the fan and affect the effectiveness of the radon-reduction system.” RadonAway's winter freeze-up bulletin describes the failure mode: ice forms in the pipe, usually at the top, from condensation created as moist air is drawn through cold pipe — and it happens on systems with long lengths of pipe exposed to the cold. Their key line: “An interior pipe system will not freeze except perhaps in extreme climates.”

Winter Is Also When Radon Peaks

The cruel timing: the season that freezes systems is the season you most need them. Health Canada states indoor radon levels are typically higher during colder months — closed windows reduce ventilation, and the stack effect (warm air rising and escaping, depressurizing lower levels and drawing soil gas in) is strongest during the heating season. Its ongoing national seasonal-variation study has found that in all regions of Canada, summer radon tests have underestimated annual radon levels. A frozen system in January is failing at the worst possible time — and it's also why winter is the right season to run your long-term test.

Canadian-Style Systems vs American Advice

Much of the radon content Canadians find online is American, and on system layout the two countries genuinely part ways:

• US practice (EPA): the exhaust fan must not be located in or below a livable area — attic, garage, or exterior — and exhaust must vent above the roof surface, 10 feet or more above ground. The EPA explicitly disallowed ground-level discharge, citing re-entrainment risk.
• Canadian practice (Health Canada): the vent pipe can terminate at either roof level or ground level, and the fan can be placed in the basement or outside the living space. A fan inside the living space is usually vented sideways through the rim joist at ground level — Health Canada compares it to the power-vented exhaust of a natural gas water heater — and notes that with fan and pipe indoors plus a ground-level discharge, “almost the entire system is located indoors, which helps to avoid problems that can arise from cold climates.” Field studies of indoor fans with near-ground discharges show the technique is effective, though Health Canada notes more field testing is needed where houses sit close together.
• The Canadian standard goes further. CAN/CGSB-149.12-2024 — the national standard for radon mitigation in existing homes — permits three discharge types (rooftop, gable-end, side-wall near ground level), and clause 5.3.2 says the side-wall discharge from a short pipe near ground level “shall be favoured in cold weather areas.” Clause 5.8.1.1 goes further still: the fan and piping shall not be located outdoors except in regions with a heating degree day (HDD) value of 3,999 or lower — which rules out outdoor fans across most colder Canadian regions.

The caveat that keeps interior installs safe: Health Canada says an indoor fan must be confirmed airtight with all joints sealed, and CGSB-149.12-2024 (clause 5.9.1) requires a leak test unless the fan is outdoors/in unconditioned space or the fan and all critical seams are under negative pressure. Done right — solvent-welded joints, fan below the discharge — an interior system is the cold-climate design, not a compromise.

Building a Freeze-Resistant System

• Keep the system indoors. The single biggest factor, per both Health Canada and RadonAway. Minimize exterior pipe; on a side-wall discharge the exhaust end must extend a minimum of 100 mm (4") from the exterior wall surface per CGSB-149.12-2024 — only a short stub of pipe ends up outdoors.
• Insulate pipe in cold spaces. The standard requires insulation on pipes in unconditioned spaces or outdoors (short exhaust stubs excepted) — minimum R4 with an exterior vapour barrier where pipe passes through an attic.
• Slope everything back to the soil. CGSB requires horizontal runs minimized and sloped at least 1% so condensate drains to the ground, with no traps where moisture can collect.
• Divert condensate around the fan. The standard requires proper condensation drainage — and where drainage isn't integral to the fan housing, a condensation bypass shall be installed. That's exactly what the RadonAway condensate bypass kit does.
• Mind the termination. The standard prohibits terminations where they'd cause hazardous ice on building or neighbouring surfaces, directly above walkways or paved driveways, or where snow clearing could bury them — and requires the pipe end be protected by low-pressure-drop stainless mesh with 10–12.5 mm openings (our stainless pipe guard), not a restrictive cap — RadonAway warns cap grates can freeze solid in cold climates.
• Pick pipe for winter. RadonAway's freeze bulletin: 4" pipe resists freezing closed better than 3", and Schedule 40 wall thickness adds insulation. Browse pipe & fittings.

Key side-wall clearances from CGSB-149.12-2024 Table 4 (required minimums): 1.8 m from a mechanical air supply inlet, 1 m from an openable window, 0.3 m above grade, 2.1 m above a paved sidewalk or paved driveway located on public property, and 1 m horizontal clearance from any area below the discharge where falling ice could injure someone.

How to Tell Your System Has Frozen

Per RadonAway, the classic signature: the fan keeps running normally, but the u-tube manometer reads zero or has dropped well below its usual mark — any sustained change from the labelled start-up baseline means the system isn't moving air, and in winter, ice is the prime suspect. (CGSB-149.12-2024 requires that start-up pressure be marked on a durable label precisely so you have a baseline; it also requires a performance indicator readable — or audible — indoors.) The fix per RadonAway: disassemble the pipe to clear the ice, or wait it out — sun and fan-motor warmth will eventually clear it when weather moderates. If freeze-ups keep recurring, the system layout is the problem: too much cold pipe. An audible system alarm catches the suction loss the day it happens.

Frequently Asked Questions

Can a radon fan be installed in the basement in Canada?

Yes. Health Canada's guide explicitly allows the fan in the basement with a sideways rim-joist discharge at ground level, provided the fan and joints are confirmed airtight — and the Canadian standard requires a leak test for interior installs unless the fan and critical seams are under negative pressure. This differs from US EPA practice, which keeps fans out of livable space.

Why does my manometer read zero in winter but the fan still runs?

That combination is the classic frozen-pipe signature per RadonAway: ice — usually at the top of the pipe — has blocked airflow while the fan spins on. Clear the ice or wait for a thaw, and fix the underlying exposure of pipe to cold.

Should a Canadian radon system vent above the roof?

It may — rooftop and gable-end discharges are permitted — but CAN/CGSB-149.12-2024 says a side-wall discharge near ground level shall be favoured in cold weather areas, because it keeps almost the whole system warm and drains condensate before it can freeze.

Are radon levels higher in winter?

Typically yes — Health Canada attributes it to reduced ventilation and the stack effect, and its national seasonal study found summer tests underestimated annual radon levels in all regions of Canada. Test during the heating season.

Sources

• Health Canada — Radon: Reduction Guide for Canadians (condensation and ice, fan placement, ground-level discharge, airtightness)
• CAN/CGSB-149.12-2024 — Radon mitigation options for existing low-rise residential buildings (discharge types 5.3.1, cold-weather side-wall preference 5.3.2, outdoor fan restriction 5.8.1.1, condensation bypass 5.8.1.2, insulation 5.2.1.11–12, slope 5.2.1.7, termination and clearances 5.3.4–5.3.5.7 and Table 4, leak test 5.9.1, performance indicator 5.11)
• RadonAway — Mitigation System Winter Freeze-ups (freeze mechanism, symptoms, fixes, prevention)
• Health Canada — Guide for Radon Measurements in Homes (winter levels, stack effect)
• Health Canada — Seasonal Variation Study (summer tests underestimate)
• US EPA — Consumer's Guide to Radon Reduction and EPA roof-venting FAQ (US practice, for contrast)