exhaust fans

Bathroom and kitchen exhaust fans provide basic ventilation and are an excellent way to avoid moisture and odors. Be aware, however: since exhaust systems removes stale air from our homes, they may also create negative pressures within the house, which should be compensated in airtight homes.

Moisture & Exhaust fans

Bathroom and kitchen exhaust fans remove moist air, and helps prevent and solve problems like mildew, mold and odors. You just have to run the exhaust fan during your showers, baths and cooking, and some minutes (20 minutes?) after.

Every home should have a high-quality exhaust fan in each bathroom and in the kitchen, duly ducted to outdoors, even if it has a Heat Recovery Ventilator (HRV) or a Energy Recovery Ventilator (ERV) system.

Exhaust Fans and Home Insulation Levels

Since exhaust systems removes stale air from homes, they tend to create negative pressures within the house.

New fresh air should be brought into the home, which is often accomplished through air leaks. That is: exhaust systems work well, without the need to bring mechanical fresh air, in moderately airtight homes. But in superinsulated airtight homes they demand a mechanical ventilation system to bring fresh air into the building.

Without it, exhaust fans can cause backdrafts, a rare but dangerous situation.

Backdrafts

Backdrafts happen when gas, fuel or wood combustion appliances compete for air with exhaust fans. Exhaust fans may pull the combustion gases back into the rooms and living space, creating air pollution and potentially very dangerous situations.

To avoid them, homes should be loosely airtigh (which isn't necessarily a problem in hot and eventually in moderate climates) or should use fresh air supply systems (mechanical ventilation).

The last solution is the only truly solution in cold climates and hot humid climates.

Exhaust Fans and Climate

In climates where energy efficiency and comfort demand highly insulated and air-tight buildings (cold climates, hot humid climates...), exhaust systems should be part or complement a wider mechanical ventilation, able to provide fresh air to the house and compensate the stale air removed by exhaust fans.

See: Mechanical Ventilation Systems

Central Exhaust Systems

Besides simple bathroom and kitchen exhaust fans, there are also central exhaust-only systems. These central ventilators are often installed in attics, crawl spaces and basements, with their ducting leading to bathrooms, kitchen and other rooms.

Central exhaust systems are reliable, cheap and very useful systems, able to extend the role of simpler systems. However in most cases they don't replace spot ventilation, that is, bathroom and kitchen room exhaust fans.

It's usually advantageous or necessary to have also separate kitchen (and bathroom) exhaust fans, since central exhaust systems aren't designed to respond to specific room needs or designed to accommodate the grease associated with the kitchen area.

Exhaust Fans

When shopping prefer a Energy Star or other officially labeled exhaust system. To compare models, pay attention to the quietness of the model (measure in Sones; 0.5 Sone is common in new-efficient models) and its capacity (Cubic Feet per Minute - CFM - or Litters per Second: L/s).

See, for more details: Choosing/Buying Bathroom Fans