How do I ventilate a heated garage to prevent moisture buildup in NB winters?

Proper ventilation in a heated NB garage requires a combination of controlled mechanical exhaust and passive or mechanical makeup air to remove moisture without wasting all your heat. This is one of the most overlooked aspects of garage construction in New Brunswick, and failing to address it leads to chronic condensation on walls and ceiling, rusting tools and vehicles, mould growth behind drywall, and deterioration of stored belongings.

The moisture problem in a heated NB garage is uniquely intense. Every time you drive a snow-covered vehicle into a warm garage during our six-month winter, kilograms of snow and ice melt and evaporate into the garage air. Road salt and brine accelerate the melt rate. A single vehicle can release 2 to 4 litres of water into the garage air after a winter drive, and if you have two vehicles, that is potentially 4 to 8 litres of moisture per day entering a space that may only have 80 to 100 cubic metres of air volume. Without ventilation, this moisture has nowhere to go except into your walls, ceiling, and belongings.

The most effective ventilation strategy for a heated NB garage is a through-wall or ceiling-mounted exhaust fan paired with a passive makeup air inlet. A bathroom-style exhaust fan rated at 80 to 150 CFM (cubic feet per minute) installed on an exterior wall or through the roof is the minimum for a two-car garage. For a workshop where you also generate dust, fumes, or additional moisture, a 200 to 300 CFM fan is more appropriate. Install the exhaust fan on the wall opposite the garage doors, positioned high on the wall or in the ceiling where warm, moist air naturally accumulates. The passive makeup air inlet — a simple 4 to 6-inch insulated duct with a gravity damper — should be installed on the opposite wall, low to the ground, to create a cross-ventilation path that sweeps moisture-laden air across the space and out through the exhaust.

Timer and humidistat controls make the system practical for NB winters. You do not want the exhaust fan running continuously because it pulls your expensive heated air outside. A humidistat (humidity-sensing switch) set to activate the fan when relative humidity exceeds 50-55% is the most energy-efficient approach — the fan runs only when moisture levels are actually elevated, typically for 30 to 90 minutes after vehicles are brought in. Alternatively, a simple timer switch that runs the fan for 30 to 60 minutes after you park is a low-cost, effective approach. Many NB homeowners set their exhaust fan on a timer that activates when they arrive home and runs for an hour.

For serious workshop garages or garages where moisture problems are persistent, consider a heat recovery ventilator (HRV). An HRV exhausts stale, moist air while recovering 70-85% of the heat from that exhaust air and transferring it to the incoming fresh air. This means you get effective moisture removal without the heating penalty of a simple exhaust fan. A small HRV unit suitable for a two-car garage costs $800 to $2,000 for the unit plus $500 to $1,500 for installation. While this is significantly more expensive than a $150 exhaust fan, the energy savings in NB's long heating season can pay back the difference within 3 to 5 years if the garage is heated daily.

Passive ventilation through soffit and ridge vents is essential for the attic space above the garage ceiling but does not ventilate the garage interior itself. These vents prevent ice dams and moisture accumulation in the roof structure by keeping the attic cold and dry, but they do nothing to remove the moisture inside the heated garage below. You need both systems — attic ventilation above the insulated ceiling, and interior ventilation within the heated garage space.

A few practical tips for NB garages specifically: keep a squeegee or floor drain near the garage doors to manage meltwater that pools on the slab rather than evaporating. Brush heavy snow off your vehicle before pulling into the garage — removing even half the snow before entry dramatically reduces interior moisture release. And never leave the garage door cracked open for ventilation in winter — this wastes enormous amounts of heat, creates uneven temperatures that promote condensation in specific spots, and can freeze your garage door tracks and weatherstripping.

The cost of a proper garage ventilation setup — exhaust fan, makeup air inlet, and humidistat control — is approximately $300 to $800 for materials and $400 to $1,000 for professional installation. This modest investment protects your garage structure, your vehicles, your tools, and your health. Find qualified HVAC and garage contractors through the New Brunswick Construction Network at newbrunswickconstructionnetwork.com.