Why Winter Leaks Happen More Often
In winter your furnace runs far more than in any other season, and a high-efficiency condensing furnace makes the most water exactly when it works hardest. So winter both produces more condensate and adds cold-weather failure modes — frozen lines and frozen exhaust terminations — that simply do not exist in July.
If your furnace only ever leaks in the cold months, the cause is almost certainly tied to condensate handling: the trap, the drain line, the pump, or a frozen run of tubing. The first job is to figure out which, because a frozen line and a clogged trap look similar but need different fixes. Across Greater Vancouver, a cold snap after weeks of mild weather is a classic trigger for the first winter leak.
Frozen Condensate Lines and Vents
When part of the condensate drain runs through an unheated space — a cold crawlspace, an exterior wall, or out to an outdoor termination — a hard frost can freeze the water inside it. The ice blocks the line, condensate backs up, and the furnace either leaks from the trap or shuts down on a safety switch. The Lower Mainland's freeze-thaw winters make this surprisingly common in older homes and additions.
A frozen or iced-over exhaust/intake termination outside causes related trouble: the furnace cannot vent or prove draft, so it short-cycles and condensate accumulates. You can safely check the outdoor PVC terminations for frost, ice, or snow drift and clear loose snow away from them. What you should not do is apply open flame or boiling water to indoor lines. If a section is frozen inside a wall or crawlspace, or the furnace keeps shutting down, call 604-359-1081 to have it thawed and the routing corrected so it does not recur.
Clogged Traps, Pumps, and Heavy Run-Time
Because the furnace runs almost constantly in winter, any partial blockage in the condensate trap or line that you got away with in fall now overflows. Sediment, scale, and biofilm collect in the trap; under heavy winter load the backed-up water has nowhere to go and spills onto the floor.
Condensate pumps also feel winter's strain. A pump that was marginal in autumn can fall behind or fail when condensate volume peaks, overflowing its reservoir. If you have a pump, confirm it is plugged in and cycling. Beyond that, a furnace running this hard exposes any weak fitting or cracked hose. These are routine repairs — clearing and re-trapping the drain, or swapping a pump or tubing — but they should be done before acidic water damages the cabinet and floor.
Don't Confuse a Humidifier or AC Coil
Two non-furnace sources fool people every winter. If you have a whole-home humidifier mounted on the furnace or ductwork, it uses water — and a stuck solenoid valve, clogged drain, or misaligned water panel can drip onto or beside the furnace, looking exactly like a furnace leak. Humidifiers run in winter, so a winter-only leak near the furnace bonnet often turns out to be the humidifier.
The AC evaporator coil in the cabinet above the furnace should be dry in winter, but if its drain pan holds leftover summer water or debris, a thaw can release it. Checking whether the water originates above the furnace (coil or humidifier) or below (condensate trap) is the single most useful clue you can give a technician.
When to Call and What It Costs
Call promptly if the leak is more than a slow contained drip, if the furnace is shutting down, or if you cannot locate the source. Turn the furnace off at its switch, mop up standing water away from electrical parts, and note where the water starts. Have your furnace brand and any error code ready.
Furnaces are serviced by our parent company, CanroHeat, whose Red Seal–certified technicians cover the entire Lower Mainland and prioritize winter no-heat and leak calls. Costs depend on the cause — thawing and re-routing a frozen line, clearing a trap, or replacing a pump or humidifier valve all differ — so we diagnose first and give you an exact written price. Call 604-359-1081. And if a leak ever appears with soot, a CO alarm, or a gas smell, leave the home and call FortisBC at 1-800-663-9911 or 911 first, then call us.