Keep humidity under control Because relative humidity affects comfort, tailoring the humidity in your house to the season reduces the use of energy for heating and cooling.  For most people, a relative humidity of around 60 percent in winter permits a thermostat setting for heat that would be too low in dryer air.  In summer, a relative humidity of around 40 percent allows a thermostat setting for air conditioning that would be uncomfortably high in humid air. Both air conditioners and furnaces dry the air in your house.  In summer, that’s usually ok, but in winter and during summers in desert like climes, the air often becomes too dry.  The solution is to install a humidifier at the furnace or to purchase a stand-alone unit.  If the air in your house is uncomfortably damp despite heating and air conditioning, consider buying a dehumidifier to pull additional moisture from the air.

At least once a month, check the filter in a forced-air heating and cooling system
A dirty filter can raise your furnace or air conditioner’s energy consumption by 5 to 15 percent.  Furnace overheating that can result from a clogged filter can shut down the system completely.  Monthly replacement may be necessary even if the manufacturer of the filter you buy advertises that it works much longer than 30 days.  The fine mesh of many such filters can actually fill more quickly than that of less effective ones.  To check a filter, simply extract it from its slot near the blower.

Clean your heating and cooling system vents
Dust on the registers in a forced-air system can cut its efficiency by 10 percent or more.  The same goes for dust on baseboard heaters and radiators.  Vacuum these parts of your heating system regularly using a brush nozzle.  Unscrew registers from walls and vacuum accessible surfaces inside the ducts.  Use a flexible hose rather than a metal or plastic wand, and fasten the brush securely to the hose with duct tape.

Remove dust buildup from the blower of a forced-air heating system
Despite the filter in your furnace, the blower that circulates air throughout the house can become caked with dust, reducing its efficiency.  Wipe and vacuum dust from the blower blades and the walls of the blower chamber two or three times a year.

Release trapped air from radiators and convectors
Steam and hot-water heating systems lose effectiveness when air pockets develop in the radiators or convectors.  Bleed the air from these components at the beginning of each heating season and whenever you hear the telltale knocking produced by air lodged in the system.

Don’t pay to heat or cool an empty house
Lowering this thing one degree can shave 3% off your bill. There’s no point in heating or cooling an empty house or apartment when you leave home for a weekend or longer.  Save money in warm weather by setting your thermostat to 85 degrees, or simply turn the AC off.  In cool weather, wet the thermostat to 65 degrees or lower.  Reset or reprogram the thermostat upon your arrival home.

Close the registers or turn off radiators in an unused room
Stopping the flow of heated or cooled air to a room, then shutting the door to isolate it can save 5 to 10 percent of your heating and cooling costs.  There are a couple of exceptions, however.  Unless you have electric baseboard heating with a thermostat in every room, you may not be able to seal off a room fitted with a thermostat.  In that case, closing the door often raises or lowers the temperature in other parts of the house controlled by the same thermostat.  Also, if you heat your house with a heat pump, closing registers causes a heat pump to run inefficiently and might harm it.

Turn off exhaust fans as soon as the need for them passes
Exhaust fans excel at extracting heat and moisture laden air from kitchens, bathrooms, and laundry rooms.  Indeed, they are so effective that, in an hour or two, they can expel an entire houseful of warmed or cooled air.  To save energy dollars, run exhaust fans no longer than necessary to do their work.

Open doors inside the house to maximize heating and cooling efficiency
Whenever possible, leave doors between rooms open to assist air circulation.  Exceptions are houses with more than one thermostat, such as those with electric baseboard heating or two furnaces and air conditioners that serve different parts of the building.  In such cases, close doors that join areas controlled by different thermostats.

Move home furnishings and other appointments away from forced-air registers
For maximum heating and cooling efficiency, don’t trap costly heated or cooled air behind sofas, drapes, and similar obstructions.  Keep drapes near registers open as much as possible, and re-arrange furniture to promote air circulation.

A lighter or darker colored roof could save you money
When the time comes to replace an asphalt-shingle roof, your choice of color can affect your energy bill.  In mostly warm, sunny regions, a light-colored roof that reflects heat is the best choice.  If you have long, cold winters, consider a dark roof to absorb heat from the sun.  The right choice can save up to 10 percent on energy costs.

Keep sources of heat away from your thermostat
A lamp or even a TV set placed near a thermostat can waste valuable energy by fooling this sensitive instrument into concluding that the temperature inside your entire house is what the thermostat is sensing.  As a result, the thermostat turns on the air conditioner unnecessarily.  To avoid this, keep incandescent lamps and other electric appliances at least 4 feet from the thermostat.

Use ceiling fans
Overhead fans with variable speeds, reversible rotation, and variable-pitch blades optimize heating and cooling, especially in rooms with high ceilings.  Most fans replace a light fixture, whose anchorage in the ceiling may need strengthening to support the often substantial weight of a ceiling fan.
In summer, use the fan to lift cool air toward the ceiling from the floor.  This approach is especially helpful in rooms cooled by window units or floor registers in a central air-conditioning system.   Reversing the fan in winter helps circulate warm air trapped against the ceiling.

Shield your air conditioner from the sun
An air conditioner running in the shade uses as much as 10 percent less electricity than it would consume in the sun.  If possible, put the air conditioner’s outdoor heat exchanger, called the condenser, on your home’s shadiest side.  If you plant trees and shrubs to keep your air conditioner cool, take care not to block the flow of air to the condenser.

Add a reflective surface to the wall behind radiators
If your house has radiators or baseboard convectors fed by hot water or steam, you can increase heating efficiency by taping sheets of aluminum foil or foil-covered illustration board to the wall behind each of them.  The foil prevents heat from being absorbed by the wall and reflects it back into the room.  Don’t use this technique with electric baseboard heat; it may create a shock hazard!

Slow the escape of heat through the glass in windows and doors.
If you live in a region with cold winters, and your home has a large expanse of glass, hang insulating curtains or draperies in front of windows and glass doors to reduce heat loss, especially at night.

Close the fireplace damper
Leaving a fireplace damper open is like keeping a window wide open day and night and can account for 5 to 15 percent of your total energy cost for heating.  Close the damper when the fireplace is not in use and seal openings around the firebox and hearth with caulking material specially formulated for use in fireplaces.

Match the air conditioner to the room
Choosing an air conditioner of the correct capacity for a room assures that you get the most from your energy dollar.  Select a unit according to the total area to be cooled.  Air-conditioning capacity, a form of refrigeration, is measured either in British Thermal Units per hour or in tons. (A ton of refrigeration absorbs in 24 hours a quantity of heat that would melt 2,000 pounds of ice, about 240,000 BTUs) A 1-ton unit is comparable to one rated at 10,000 BTUs per hour.