This whole house exhaust fan from Tamarack Technologies will slowly reduce the indoor air temperature of smaller to modest-sized homes (600 to 1,500 square feet). Turning the fan on in the evening during hot, summer months will gradually exhaust the stale air in the house through existing attic vents allowing cooler, outside air to be drawn in on the lower floors. Unlike conventional whole house fans that draw thousands of cubic feet of air per minute and help occupants feel cooler by creating a breeze, these fans move air much more slowly - gradually lowering the indoor air temperature with cooler outdoor evening air over the course of many hours.When not in operation, the automatic motorized insulated door assembly (R-22) a closes tightly over the fan to provide an airtight seal. The door requires about 30 seconds to fully open or close. The 14" x 24" white grill attaches to the ceiling below for a clean, finished appearance. The fan will sit on either 16" on center or 24" on center rafters with no rafter cutting. It may be mounted vertically to exhaust from cathedral or vaulted spaces. In the attic, sufficient free air ventilation is required to exhaust the air being pushed into the attic from the fan. In the case of this fan, this means a 1 to 2 square foot screened opening or equivalent. In order to physically carry the fan into the attic, a 10 by 19 inch (or larger) open is required.