The HRV
Most Toronto houses built since the energy codes tightened have an HRV in the basement, and a large proportion of them have never been touched.
Short answer
A heat recovery ventilator brings in outdoor air and exhausts stale indoor air through a core that transfers the heat between the two streams. It needs the filters cleaned every few months, the core washed annually, the exterior hoods and the condensate drain checked, and the balance verified. Neglected, it stops ventilating and the house gets damp.
What it needs and how often
Filters: cleaned or replaced every two to three months during the heating season, which is the item most often never done.
Core: removed and washed annually, which on most units is a straightforward homeowner job once somebody has shown you.
Exterior intake and exhaust hoods: screens cleared of lint, leaves and insect nests, and checked for ice blocking in winter.
Condensate drain and trap: checked, because a blocked drain on an HRV backs water into the cabinet.
Grilles and the duct runs to them, which collect dust like any duct.
And the balance between supply and exhaust, which is a technician task and which is frequently out from the day of installation.
What happens when it stops working
Indoor humidity climbs through the winter. Windows run with condensation. The bathroom stays damp. Mould appears on window frames and in closets on exterior walls. In a tight modern Toronto house the HRV is the ventilation, and when it stops the house has none — which is the cause of a great many winter moisture complaints.
Signs yours is not working
Window condensation through the winter, which is the clearest single sign.
Indoor humidity reading above the sixties in January, which in a Toronto winter means ventilation rather than a dehumidifier.
Stale air and lingering cooking smells.
A bathroom that does not clear after a shower.
Ice at the exterior hood, or an intake hood you cannot find at all.
And a unit that is silent, which on many installations means somebody switched it off because it was noisy or because the heating bill looked high.
Running it properly
Leave it on. An HRV switched off is a ventilation system that is not ventilating, and the running cost is modest.
Use the dehumidistat or the control as intended, and understand what the settings actually do — many homeowners have never been shown.
Boost it during showers and cooking if the control allows.
Keep a hygrometer and manage to a number: in the thirties to low forties in a Toronto winter.
Clean the filters on a schedule you will actually keep, which is the whole game.
And get it balanced and serviced properly once, because a correctly balanced unit is quieter and more effective and most of them have never been checked.
Common questions
How often do HRV filters need cleaning?
Every two to three months during the heating season.
Should the HRV be left running?
Yes. Switched off, the house has no ventilation, and winter moisture problems follow.
What reading should the house sit at in winter?
Thirties to low forties in a Toronto winter, measured rather than guessed.