Your HRV in Winter: What Ventilation Actually Costs, and the Settings That Waste the Least Heat

Save daily · Published 2026-10-31 · Last updated 2026-10-31

General information only, not financial advice. Worked examples use one named unit's rated figures and clearly labelled assumptions; rerun the arithmetic with your own unit's ratings and your own electricity rate before acting on it.

Switching the HRV off for winter looks like the thrifty move. It is usually the expensive one — priced in window condensation, stale air and moisture loading into the house instead of dollars on a bill. The honest question is not whether ventilation costs anything; it does. The question is how much, in numbers, and which settings pay the least for the same fresh air. That takes a teardown, and a teardown needs a specimen. This guide uses one rated unit throughout: a Broan HRV250 ECM, rated at 50–250 CFM, drawing as little as 18 watts at 64 CFM, with a rated sensible recovery efficiency of 75 percent at 0°C and 66 percent at −25°C (s1). Smaller units — a vänEE 40H+ covers homes needing up to 77 CFM (s6) — scale the same arithmetic down with their airflow.

Cost line one: the fan, smaller than you think

At the 64 CFM setting, the specimen unit's fan draw is 18 watts (s1). Run continuously for a 30-day month, that is 18 W × 24 hours × 30 days — about 13 kWh. At an assumed 15 cents per kWh — an assumption, not a rate quote; substitute your own — the fan line is roughly $2 a month. Even a considerably thirstier unit at this airflow does not change the shape of the answer: the fan is the small line on this bill.

Cost line two: the heat the core does not recover

The real cost of ventilation is thermal. Every cubic metre of fresh air the HRV brings in must be brought up to room temperature; the core recovers part of that heat from the outgoing stream — 65 to 85 percent or more across HRVs generally (s3), 75 percent at 0°C and 66 percent at −25°C on the specimen's rating (s1) — and the heating system pays for the rest. Here is the deep-cold arithmetic, assumptions on the label:

Read that table both ways. Ventilation in deep cold is not free: about 330 kWh a month at continuous low speed in this example. But without recovery, the same fresh air would cost the full 1,040 kWh. The HRV is not the expense in this picture — it is the discount on an expense the house takes on the moment it ventilates at all.

Continuous vs 20/40: the setting that moves the real line

The intermittent mode most controls offer runs the fan 20 minutes in each hour and rests it for 40 (s4). One-third the runtime cuts both cost lines by roughly two-thirds, because both scale with operating hours:

So the decision is not really continuous-good or intermittent-bad; it is how much ventilation the house actually needs this month. A full house generating cooking, shower and laundry moisture through a cold snap earns continuous running. A two-person household in a mild spell is buying air changes it may not need at continuous speed — and the sources are blunt that over-ventilating in winter backfires: running continuously on low can overdry a home that already runs dry, and the furnace works longer against the extra cold air (s3). The control most manufacturers intend for winter is the humidity dial: set it to the maximum indoor humidity the house should hold through fall, winter and spring, and let sustained window condensation — not habit — argue for more runtime (s3, s5).

What defrost is doing to your ventilation (and your bill)

In persistently cold weather, moisture in the outgoing air can freeze inside the core and block the exhaust stream. HRVs handle this automatically: a damper closes off the outdoor supply and warm indoor air is run through the core to melt the ice — and during defrost, the indoor–outdoor air exchange pauses (s2). Some units defrost by recirculation instead (s6). The specimen's own spec sheet schedules defrost in minutes against exchange minutes, up to 6 minutes of defrost inside a 40-minute cycle at its coldest settings (s1): in deep cold, up to roughly a seventh of the hour may be defrost rather than ventilation. That is normal operation, not a fault — and it is why deep-cold ventilation never quite delivers its nameplate airflow. One defrost design does carry a real cost warning: units that defrost with an electric pre-heater spend significantly more energy and recover less heat while doing it (s2). A household pricing a replacement unit for a cold climate should ask which defrost method it uses before asking about anything else.

The October reset that keeps the rated numbers real

1. Clean or replace the filters. Dust-loaded filters restrict the fresh-air supply (s5) — the unit delivers less air than its setting promises.
2. Check the core and the drain. A dirty core transfers less heat, so the recovery percentage in the teardown quietly falls (s5); the condensate drain must be clear before freeze-up season (s2).
3. Walk outside and clear both hoods. Snow, ice, leaves and lint at the intake and exhaust hoods choke the system; recheck after storms and long cold snaps (s5).
4. Set the winter control deliberately. Humidity dial to the house's winter ceiling, mode chosen for the household's actual moisture load — continuous or 20/40 — rather than whatever it was left at in June (s3, s4).

What success looks like: windows stay clear through a cold snap without the house feeling dry enough to crack lips and woodwork, supply grilles deliver a perceptible flow on schedule, and the only interruptions are the brief, regular defrost pauses. Persistent window condensation, water leaking from the cabinet, visible ice inside the unit, or a fan that stops or turns loud are not settings problems — those are service calls (s5).

Questions that come up every winter

Should the HRV just be switched off until spring? That zeroes both cost lines and the ventilation with them. In a tight house, the moisture from showers, cooking and breathing then has nowhere to go; the bill arrives as condensation and mould risk instead of kilowatt-hours. Off is a setting for summer on some controls (s3), not a winter economy.

Does this math cover ERVs too? No, deliberately. An ERV transfers moisture as well as heat, which changes the winter trade-off; every figure here is HRV-only, from an HRV's rated spec sheet (s1).

Why does the house feel drier with the HRV running? Winter outdoor air holds very little moisture; bringing it in and warming it drops indoor relative humidity, and running more ventilation than the house's moisture production requires overdrys it (s3). The fix is the runtime decision above, not a bigger humidifier fighting the ventilator.

— Penny Hughes, Money Writer — Saving Desk