» Humid outdoor air is leaking into the house...
through cracks around doors and windows, electrical outlets, ducts, vents or fireplace dampers that don't seal tightly. In Florida homes about 38% of the air conditioner's work (and operating cost) goes to drying out this moist air leaking in from out of doors. Leaks in the ducts that supply cooled air to rooms will make this situation much worse, because the overall house air pressure becomes "negative' with respect to the out of doors whenever the air conditioner is running. In this condition the house sucks in warm, moist air whenever the air conditioning system runs. The system runs longer to compensate. Even more warm air is drawn in, which needs to be cooled......and so forth in a vicious cycle. Costs rise significantly.

» The house is equipped with jalousie or awning windows designed for cross ventilation...
Instead the house is closed up for air conditioning. Or almost closed up: Unfortunately, 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.

» A rooftop power ventilating fan pulls hot air from the attic on summer days...
but a). The fan's thermostatic control is set too low (maybe 95 degrees instead of 115 degrees), so the fan runs more than it should; b). There's a lot of air leakage from the house across the ceiling to the attic, or bathroom and dryer vents open into the attic instead of passing through the roof, so that when the rooftop fan pulls air from the attic it also pulls air (expensively cooled air) from the house; and c). The fan motor itself is costly to run, and eats up any potential savings for having cooled the attic. In general, well insulated attics don't need power ventilation. Passive ventilation devices such as high ridge, off-ridge, turtle-back or gable vents, together with low soffit vents, are adequate. The optimum design is usually a ridge vent (internally baffled so that rain doesn't bounce in) and soffit vents.

» Doors need weather-stripping...
to prevent significant air leakage. The crack around all four edges of a standard door is 20 feet long. If the crack is 1/12" wide, the total "hole" size is 20 square inches, roughly the equivalent of a softball sized hole in the door! If the house is negatively pressured whenever the air conditioner runs because of supply duct leakage (see #33), that size hole admits a lot of warm, moist air for the air conditioner to cool and dry. A wide variety of weather-stripping materials are available at local hardware stores and home supply centers. You'll often find good instructions there too, either from staff or from how-to booklets.

» Windows and doors need caulking...
to prevent air leakage, for the same reasons discussed above. This is do-it-yourself work. Caulk is cheap, applying it is easy, but it takes time. Caulk cracks around window and door frames; cracks where masonry walls meet wood siding or trim; wall penetrations by pipes, meter box, dryer vent or exhaust vents, etc. Some all-purpose caulks are silicon, silicon-acrylic and siliconized acrylic latex.

» The garage was converted to a family room...
without insulating the walls or ceiling. Now it's the hottest room in the house, and that's where the TV is located and the family spends the most time. To make it comfortable, the family turns down the thermostat setting for the whole house. Costs rise.

» In the hallway ceiling there's a large whole-house fan with incompletely closed louvers...
It provides a major site of air leakage to or from the attic. If you have one of these fans and never use it, you'd do well to seal it from above and drape it with blankets of insulation.

» Old casement or awning style windows are deformed out of alignment and will not seal shut...
allowing warm moist air to leak in, or expensively cooled air to leak out.

» The house lacks shade on the east or west sides, or a mobile home sits fully exposed to the sun...
Shade trees can reduce air conditioning costs by up to 30%, and higher if it's a mobile home.

» Windows lack inside shading devices (shades, drapes or blinds), or the devices are not consistently operated...
These shading devices are tremendously important. Use them to block heat entry during summer days.