HRV and ERV Settings for Wetter Windows

• What an HRV or ERV is doing
• When wet glass points at ventilation habit
• Practical checks before you change hardware
• HRV vs ERV for condensation
• When to call a technician

Many newer Canadian homes have an HRV (heat recovery ventilator) or ERV (energy recovery ventilator). These bring in outdoor air while limiting heat loss. They also move moisture — sometimes in helpful ways, sometimes not. Wet windows often show up when the unit is off, unbalanced, or set for a season that no longer matches the weather.

§What an HRV or ERV is doing

Both continuously (or on a schedule) exhaust stale indoor air and supply fresh outdoor air through a core that recovers heat. An ERV also transfers some moisture between the streams; an HRV mainly transfers heat. In deep cold, outdoor air is very dry, so continuous fresh-air exchange often lowers indoor humidity. In mild, damp shoulder seasons, outdoor air can be humid enough that ventilation alone will not dry the house.

§When wet glass points at ventilation habit

• The unit is switched to intermittent or off overnight while bedrooms stay closed — moisture from people builds and shows on cold panes by morning.
• Filters or cores are clogged, so little air actually exchanges even though the fan runs.
• Supply and exhaust are badly unbalanced, so some rooms get little fresh air while moisture stays put.
• Bathroom and kitchen fans are rarely used, so local steam never leaves and the HRV/ERV cannot keep up alone.

§Practical checks before you change hardware

• Confirm the unit is powered and set for continuous low or a winter schedule that runs overnight, not only when someone remembers a boost button.
• Replace or clean filters on the interval in the manual; a dirty filter is a common “it runs but nothing changes” cause.
• Use a hygrometer in the wettest room: if overnight RH climbs while the ventilator is off or on intermittent, try continuous low for a few cold nights and compare morning glass.
• Keep using bathroom and range exhaust for showers and cooking — whole-house recovery ventilation is not a substitute for source exhaust.
• If defrost cycles are frequent in extreme cold, read the manual: some modes reduce outdoor-air volume temporarily; that is normal protection, not a reason to shut the unit off for weeks.

§HRV vs ERV for condensation

In a dry Canadian winter, both can help by diluting indoor moisture with cold outdoor air. An ERV may hold a bit more indoor moisture than an HRV in the same conditions, which can matter if your home already sits above its dry line. Neither unit “cures” failed sealed glass, unvented laundry, or a humidifier left on high. Match expectations to physics: lower room dew point or warmer glass — ventilation mainly helps the first.

§When to call a technician

If continuous operation, clean filters, and source exhaust still leave whole-home RH high, or if you suspect the system was never balanced after renovations, get the airflow checked. Do not block outdoor intakes or exhausts to “stop drafts.” Combustion appliances and make-up air need qualified attention if you are unsure.

Start with overnight run mode, clean filters, and a humidity log. Treat the HRV or ERV as one moisture lever among source control, glass warmth, and room air mixing — not the only fix.

Originally published at https://dry-glass-notes.surge.sh/articles/hrv-erv-wet-windows.html (AI-assisted, sources cited). If this helped, zaps go to hollisvarrow3753@coinos.io.