Different Types of Fans
Attic Fans
Though they’re a popular way to cool down attics in the summer, studies have shown that most attic fans actually cost more in electricity than they save in air conditioning costs. One exception is an attic fan driven by its own solar panel, which of course costs nothing in electricity. One reason that attic fans are inefficient is that they rely on the existing attic vents (at the soffits, ridge, or gables) to make up the air they exhaust. Usually, these attic vents are not designed for this purpose, and they may not be able to supply enough replacement air. That can put the attic at a lower pressure than the upper floor of the house, which sucks conditioned air into the attic through holes for recessed lights, attic stairs, whole-house fans, and the like. Conditioned air can also be sucked directly out of unsealed ducts in the attic. In this situation, adding attic fans can cost you more cooling dollars than not having a fan.
Ceiling Fans
As a way to move air to keep cool, ceiling fans can be a welcome relief in the summer. They’re available in many styles; most have light kits as an option, and some even have remote controls. If you install a ceiling fan on a porch, make sure it’s rated for outdoor use. Otherwise, moisture-sensitive fan blades will droop with time, and the electrical portions of the unit will corrode quickly, particularly in marine environments. If no one is in the room, a ceiling fan offers no cooling. In fact, the waste heat generated by the motor actually warms the room slightly. Because they’re heavier than a light fixture and they move, code requires ceiling fans to be hung from special electrical boxes that are rated for the load.
Bathroom Exhaust Fans
Every bathroom should have a fan, mainly to exhaust excess moisture. Particularly in the winter, the warmth inside a house tends to drive moist air out through whatever passage it can find. Moist air that isn’t removed by a fan and ducted outside will find holes in walls or ceilings (even the tiny space around an electrical box will allow air to pass through), where the moisture can condense against the first cold surface it encounters. That moisture can then cause rot and mold growth. By code, bath fans must vent outside through a duct, although in many cases they are mistakenly ducted into the attic. When vented into an attic, the moisture can condense on the roof sheathing, leading to mold and rot. Instead, the fan should either vent through a wall or the roof. In cold climates, it’s a good idea to insulate these vents through the attic to prevent moisture from condensing inside the duct and draining back into the bathroom. Fans do no good if they aren’t used. Bath fans can be controlled by a regular wall switch, but for a few bucks more, humidistat activated switches are available. That way, when your teenager takes a steamy shower the fan will automatically turn on. Bath fans are available in different sizes for different sized rooms, and they come with a number of additional options, including lights, night-lights, and heaters to take the chill off on cool mornings. Also, pay attention to how loud the fan is. Loudness is measured in sones, and the lower the number, the quieter the fan. For More: How to Vent a Bath Fan Through the Roof
Whole-House Fans
Mounted in the ceiling of an upper floor, a whole-house fan creates a powerful suction that draws air in through open windows. Whole-house fans rely on the attic having sufficient ventilation to exhaust the pressure they create. They can quickly cool a house down at the end of the day in areas where the temperature drops on summer evenings. They also have disadvantages. If your climate is humid, the air you draw in will be humid as well, and might not be as cool as hoped for. A whole-house fans requires a large hole in the ceiling that can be difficult to air seal in the winter, causing heated air to leak into the attic. And finally, if you don’t open enough windows to balance the suction of a whole-house fan, it can cause combustion appliances like water heaters to backdraft dangerous exhaust gases into the house. For More: Installing a Whole House Fan
Kitchen Exhaust Fans
If you have a stove, you need a range hood that ducts outside. In part, that’s to get rid of cooking smells and moisture, but if you have a gas stove, it’s also to exhaust the toxic combustion byproducts such as carbon monoxide. Unvented range hoods are available, but they really don’t do anything beyond catching some airborne grease in their filters. Code requires range hoods to be at least as wide as the stove. Vented hoods must vent outside though noncombustible metal ducts. To save space, over-the-stove microwaves are available that also serve as kitchen fans. Adding a through-the-wall exhaust fan is another option. For More: How to Find the Perfect Range Hood
Energy Recovery Ventilators (ERVs)
Tight houses need ventilation, and the energy-efficient way to provide it is with either an ERV (energy recovery ventilator) or an HRV (heat recovery ventilator). These units work similarly, with fans drawing in fresh outside air and blowing out stale indoor air at controlled rates. The two airflows pass by each other on opposite sides of a heat exchanger. In the winter, this warms the incoming air with heat from the outgoing air. In summer, the conditioned outgoing inside air cools the incoming outside air.
Heat Recovery Ventilators (HRVs)
That is all that an HRV does. An ERV exchanges heat, but it also exchanges moisture, preserving indoor humidity in the winter, and limiting indoor humidity in the summer. HRVs cost a little less, but an ERV can contribute more to your comfort in humid climates. For More: How an Energy Recovery Ventilator (ERV) Works
