Cooling and ventilating a typical residential building is not easy. One could open several windows and hope a cooling breeze passes through the building, but it's more likely a swarm of outdoor insects will find the openings first. Standard electrical fans might cause currents of air to flow, but it will be the same stale air without ventilation. Air conditioning units can provide cooling and ventilation, but they can also be very noisy and expensive to operate. One economical solution to both cooling and ventilation problems is a whole house fan.
A whole house fan works on the principle of ventilation. Early whole house fan models were very similar to stand-alone electric fans, except they were ceiling-mounted in a wooden frame over a foyer or common area. Fresh air would be drawn in from vents cut into the outside walls of the attic. A wall switch would allow the homeowner to turn on the whole house fan in an individual area, or all of the fan units at once. This early design proved problematic in a number of ways -- the belt-driven fan motors needed frequent maintenance, the fan blades generated a lot of noise and the air would circulate unevenly.
Today's whole house fan incorporates many of the same design elements as central air conditioning units. Instead of having the main fan unit installed directly into the ceiling between joists, it is suspended inside the attic space. Several slats in the front of the fan are held shut by magnets when the blades are not turning. This creates a positive seal to prevent drafts from entering the living space through an open fan unit.
The fan blades, made from either metal or plastic, draw air into a section of flexible duct work. A small hole is cut into the ceiling to accommodate the end of the duct, which is usually mated with a metal diffuser. This diffuser is the only part of the whole house fan visible to occupants. The circular fins of the diffuser allow the forced air to circulate evenly.
A whole house fan can take the place of a more expensive air conditioning system when the ambient air temperature is fairly mild. It also acts as a ventilation system to force stale air out of the room and allow fresh outside air to enter. During winter months, a whole house fan can also keep warm air from rising into the attic area unnecessarily. Second-story rooms should also feel more temperate.
A single whole house fan should be able to circulate 1500 square feet of living space air effectively, so larger homes may need several units installed for maximum effectiveness. Most whole house fan systems rely on attic space access for easier installation. Some manufacturers suggest that outside vents are not strictly necessary for effective cooling and ventilation. As long as the air in the attic space is clean and fresh, the whole house fan should be able to keep the rest of the house supplied with cooler air for a fraction of the cost of a typical central air conditioning unit.