Umbra on whole-house fans and their righteousness
We just moved to the steamy climate of Washington, D.C., from the other Washington. Faced with our first experience using air-conditioning to cool our home, we’ve got some questions about efficiency.
The house we’re renting has a central AC unit that we can control with a thermostat. It also has a roof ventilation system that circulates air under the roof using a fairly noisy and probably pretty old and inefficient fan. Here’s the thing: The fan is on a thermostat, but there doesn’t seem to be any way to control it. (We think there’s a switch in the attic but we haven’t pulled up the ladder to find out.) Since we’re planning to use the AC only when we’re home and leave it off during the day, do you think it would be more energy-efficient to turn off the fan for good, so it doesn’t run all day long? Or is this just one of those silly trade-offs that doesn’t make much difference in the long run?
Silver Spring, Md.
If you’ve been reading my column during Keeping-Cool Theme Question Fortnight, you know the routine: Close the house down (shades, awnings, windows, appliances of all types) during the day, and open it whenever the outside temperature cools, taking strategic advantage of prevailing winds to encourage the flow of air through the house.
It sounds like you have a recessed ceiling fan at the top of your house that pulls air into a vented attic, and you have no way to turn it on and off. That’s known as a whole-house fan, and it’s a handy tool for managing the flow of cooler air through an entire house. These whole-house fans are affordable and use far less energy than air-conditioning units. Open some windows, turn on the fan, and sit back while air whisks past your skin, improving your mood and your East Coast outlook.
I have hope for your “roof ventilation” fan, and I’m choosing to think the best of your landlord/lady/whatever. Ask said landperson to send someone to service the ventilation system. Tell them you’d like to use it, but it’s noisy, and you want to be able to turn it on and off at will. Apparently these fans are noisy in general, but there may be something to be done about the bushing (which reduces friction, and thus noise, in electrical appliances) or the seating or the gasket. You also might be able to replace your uncontrollable thermostat with a timed thermostat. In that case you could leave the fan “off ” (set at a high temperature) during the day, have it operate for a few hours during the transition to evening when you will arrive home and open the shades, and off again during your peaceful slumber hours. Look at the existing thermostat and call the hardware store to see if timed thermostats are compatible.
Try everything I suggest during a hot week. You’ll still have the air conditioner. If worst comes to worst, operate the air conditioner on a timed schedule as well, and you’ll maximize its usefulness while not spending your money and everyone’s resources to cool air you’re not using. Let me know if it works out with the ceiling fan.