Causes of High Summer Utility Bills
- Windows on the southwest or west side are fully exposed to the setting sun. In newer Florida homes, sunlight heating through windows accounts for about 20 percent of the air conditioning load. In older homes, it can be as much as 30 percent. Use interior shades, drapes or blinds to reduce heat through windows by about 20 percent. External shade (from trees, awnings and sun screens) works even better.
Some newer, high-tech windows have special tints or films that reduce the amount of heat transmitted across the window into the house. Most window manufacturers now offer high-tech windows with low E coatings. This is a microscopically thin, virtually invisible, metal or metallic oxide layer deposited on a window.
In a double-paned window, the coated surface may be either the outer side of the inner glass or the inner side of the outer glass.
In Florida, the latter design works better. The coating acts to suppress radiative heat movement across the window by reflecting heat back into the home during cold weather and back to the outdoors during warm weather.
- The house has awning or jalousie windows designed for cross ventilation. The house is closed up for air conditioning. These window types are notoriously leaky. In summer, the air conditioner must toil to dry as well as cool the air, and major air leaks cause major cost increases.
- Old casement or awning style windows are deformed out of alignment and will not seal shut. Warm moist air leaks in, or cooled air leaks out, resulting in higher utility costs.
- Windows lack inside shading devices (shades, drapes or blinds) or these devices are not adjusted properly. Venetian blinds and other shading devices are tremendously important. Use them to block heat entry on summer days.
- Windows and doors are open while the air conditioner runs.
- Southwest sun exposure floods the home with radiant heat in the fall. Some homes have southwest windows that are well shaded by overhangs through the middle of the summer, when the sun passes overhead. But in the fall, afternoon sunlight (radiant heat) pours in as the sun's path passes lower in the sky. Air conditioning costs may soar unexpectedly in late September and October.