In these times of rising summer temperatures, more locals are reflexing to air-conditioning to stay cool. This, however, just contributes to increasing temperatures, if the electricity used to run the conditioner is generated from fossil fuels. I recently spoke with Scott Nyborg, my college at Allen Construction, who shared some tips on staying cool without AC.
Can you give us one inexpensive, effective way to cool our homes? Whole house fans (WHF) are a good solution in our climate of cool nights, even on our hottest days. The WHF leverages this cool nocturnal air by running the fan at end of day when the outside air has cooled down, yet the inside air is still hot. The fan quickly causes an “air change,” meaning that the indoor air is exchanged for outdoor air, thus cooling the house.
This sounds straightforward; are there pitfalls? One possible problem is that a house’s attic vents are not large enough to exhaust to the outside the big volume of hot air that a WHF pushes into an attic. Attic venting is often undersized, even when code compliant, so a professional capable of sizing air flows with vent area needs to verify. [WHFs often move air at the rate of 2,000 cubic feet per minute (CFM) — about 2,000 basketballs’ worth of air going through the fan per minute!]
The attic must be well sealed from the house. Most aren’t. If the attic floor has air leaks, the attic pressure created by the WHF can force hot air along with attic dirt and dust back into the living space, working at cross purposes to cooling, and potentially degrading indoor air quality.
Also, when the fan is turned on in the evening, it creates a negative pressure in the house. To counter, windows must be open (and not just one window) because of the large volume of air.
Any safety issues? Yes, carefully exhausting combustion gases, including carbon monoxide, to the outside — [gases] generated from gas water heaters, furnaces, cookers, etc. Many modern appliances now have closed venting systems, but older appliances often rely on natural pressure gradients to get the job done. Turning on a 2,000-CFM fan changes these pressures and can backdraft the combustion gases directly into a home — a dangerous hazard. A professional should evaluate these safety concerns.
So, in brief, with adequate venting, a well-sealed attic and no combustion gas issues, one gets a low-cost, effective cooling system that harnesses our big daily temperature swings. Thanks for enlightening us.