“Caulking the exterior of a house reduces air leakage.”
Newspaper columnists often suggest that leaky walls can be improved by filling cracks on the exterior of a house with caulk. This is bad advice, for two reasons: First, most significant air leaks are located elsewhere; and second, exterior caulk can do more harm than good.
A caulk gun in the hands of an overenthusiastic builder can be a dangerous weapon. It’s not unusual to see caulk where it doesn’t belong — for example, blocking drainage at the horizontal crack between courses of wood lap siding, or blocking weep holes in windows.
If you want to limit infiltration in a leaky house, put away the caulk gun and ladder. Instead, get a few cans of spray foam and head for the basement or attic.
“Efficiency rating labels on appliances account for all types of energy.”
Neither the annual fuel utilization efficiency (AFUE) number on a furnace or boiler label nor the energy factor (EF) used to rate gas water heaters includes any accounting of electrical energy. As a result, an appliance with a high AFUE or EF number may still be an electrical hog.
An appliance’s AFUE is a laboratory rating of its efficiency at burning natural gas, propane, or oil. The calculation accounts for typical chimney, jacket, and cycling losses — but not electricity use.
A gas furnace has several electrical components, among them the furnace fan (by far the biggest electrical load), an igniter, a draft inducer, and controls. Oil furnaces include an oil pump, an oil burner motor, perhaps a power vent unit, and a furnace fan. The AFUE gives no clues concerning the power draw required to run these electrical components, which varies from appliance to appliance.
Most furnace fans draw between 500 and 800 watts, with an annual electricity use that averages about 500 kwh per year. Furnace fans account for 80 percent of the electricity used by furnaces, so total furnace electricity use averages about 625 kwh per year. If a homeowner operates the furnace fan continuously — either to improve air mixing or to meet the needs of an electronic air cleaner — annual electricity use is much higher. Since inefficient furnace fans produce waste heat, they are particularly problematic in cooling climates.