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A vent fan plays a key role in air quality inside buildings, but if they’re overused, the venting fan can undermine the building’s energy efficiency and even safety.
Even though most vent fans are small, they are powerful. Depending on their cubic feet per minute (CFM) capacity, they can pull a fair amount of heated or cooled air from the building through their vent stacks. Worse, venting fans can also introduce hazardous gases into the indoor air like carbon monoxide, nitrogen dioxides and sewer gases. If flammable or combustible gases, fumes or dust is present, explosion proof exhaust fans may be necessary.
When a ventilation fan runs, it pulls air from the space in which it’s placed, creating negative air pressure. The intake, supply or make-up air fan will pull air inside to replace the outgoing air. It may come from the outdoors through cracks in the building’s envelope or from mechanical areas in ceilings, stairwells, or basements.
Energy Losses and Air Quality Issues
If the ventilation fans pull air from the outside in, cooling and heating costs will increase. Older buildings tend to have higher air leakage rates and less insulation, and an overused exhaust fan will drive the conditioning costs even higher.
Newer buildings typically have fewer air leaks, which means that the negative air pressure created by ventilator fans will more easily pull gases from leaking ductwork or vents. Buildings that use combustion fuels for any kind of heating are vulnerable for backdrafting. The air may also come from vent stacks for plumbing, introducing harmful waste gases into the air.
Solutions
Roof exhauster or wall exhaust fans are a necessary component in many commercial and industrial buildings, but their use should be controlled. Workers in shops or factories need to turn them off when they’re not being used. A motion detector on a restroom ventilator fan will turn it on and off automatically, as will timers.