HRV Settings for Winter: How to Actually Run Your Air Exchanger

If your home was built in Ontario in the last twenty years, or has been renovated to a decent standard of airtightness, there is a good chance there is an HRV in the basement. There is an equally good chance nobody explained what to do with it. The unit gets installed, a dial gets left wherever the installer had it, and it sits there for years either barely running or running far more than the house needs.

This is the practical version: what the thing does, which setting actually matters, what to move it to as the weather changes, and how to tell from your own windows whether you have it right.

That matters because a modern airtight house does not breathe on its own. Older houses leaked enough through the envelope that stale air and moisture found their own way out. Tighten the envelope and that stops, so moisture from showers, cooking, laundry and simply breathing accumulates. An HRV is the deliberate replacement for the accidental ventilation the house used to have.

An HRV moves heat but not much moisture, which is what makes it the usual choice for Ontario. If you are still deciding between an HRV and an ERV rather than trying to run one you already own, we cover that comparison separately.

That single fact explains most complaints. A dial left at 60 percent will almost never trigger in a dry Ontario winter, so the homeowner concludes the HRV is broken when it is simply never being asked to work. A dial left at 20 percent runs the unit nearly continuously, over-ventilates, and produces the cracked-lips, static-shock house that people blame on the furnace.

Treat that as a starting point rather than a rule. Houses differ enormously in window quality, and a home with newer triple glazing tolerates noticeably more humidity than one with older double-pane units, because the inside surface of the glass simply does not get as cold.

Drop the outdoor temperature and you drop the glass temperature with it, which lowers the humidity the room can carry before that happens. This is why a setting that was perfectly comfortable in November starts fogging windows in January. Nothing failed. The weather moved and the setting did not.

Left alone long enough, that condensation stops being cosmetic. Water sitting on sills and frames leads to staining, then to mould at the frame, then to damage to the frame itself. Adjusting a dial twice a winter is a great deal cheaper than replacing window trim.

Use the boost for the moments you are genuinely adding moisture faster than the house can shed it:

Set too high, meaning not ventilating enough: condensation on windows, a musty or stuffy smell that returns after airing out, bathroom mirrors staying fogged a long time, and in bad cases mould appearing at window frames or in closet corners on outside walls.

Set too low, meaning over-ventilating: static shocks, dry throats and noses, lips cracking, wood floors and trim developing gaps, houseplants struggling, and a heating bill higher than it should be because you are exhausting more heated air than the house needs to lose.

So a unit that periodically stops and starts in a cold snap is behaving correctly, and it is one of the most common things people call in as a fault. What genuinely warrants a look is a core frozen solid rather than lightly frosted, water pooling under the unit, an intake or exhaust hood buried in drifted snow, or a unit that stops and never resumes.

Call someone when the core stays frozen through a defrost cycle, when the unit will not run at all, when you cannot get on top of condensation even at a low setting, when the airflow at the registers is clearly weaker than it used to be with clean filters, or when the house has an unbalanced feel with doors pulling or whistling. Those point at the unit, the ductwork or the balance rather than the number on the dial.