Heating accounts for more than a third of the average annual energy bill, so it pays to make your system more efficient. Most homes in the United States are heated with either a furnace, which warms air and distributes it through the house via air ducts, or a boiler, which heats water and circulates steam via pipes to radiators. Both systems operate on nonrenewable resources (oil or gas) or electricity (which is typically generated by nonrenewables).
Air conditioners use electricity to power evaporators and condensers, which pull humidity out of the air and lower air temperature. Given how much fossil fuels are burned to heat and cool our homes, it's easy to hope for a day when all living spaces will be constructed with solar panels or wind turbines. Until then, do what you can to keep your energy footprint small.
Install programmable thermostats, which regulate the temperature in your home automatically. According to Energy Star, programmable thermostats can save you up to $150 a year. Models bearing the Energy Star logo are programmable and, unlike older manual thermostats, don't contain mercury. Place foam board with a reflective surface against the wall behind the radiator to direct heat back into the room. Keep your home cool by drawing shades and drapes on sunny days, and minimizing the use of heat-producing appliances, such as the oven and dryer.
Turn off lights you're not using, and remember that compact fluorescent lightbulbs (see Lightbulbs) burn cooler than incandescents. Open windows at the top, as well as the bottom, to allow rising heat to escape as fresh air comes in. If your house has cooled down overnight, closing the windows when you wake up can help keep the heat out for a while. Also, consider putting in ceiling fans, a time-honored, low-energy method for keeping the air moving and the room feeling cooler.
In air-heated homes, improve energy efficiency by cleaning and properly sealing ductwork. Replace flexible ductwork -- which can trap air -- with more aerodynamic metal. Hire a professional to check the efficiency of older furnaces and boilers. Upgrading a gas furnace in an average cold-climate house saves carbon dioxide emissions equal to taking one car -- driven regularly and averaging 20 miles per gallon -- off the road for four months. Putting in a new oil furnace will save the same emissions as parking that car for close to half a year.
If you have an old water heater, install an insulating jacket at least three inches thick (poorly insulated models can add an additional 4 percent to 9 percent to your heating bill each year). You can also invest in a tankless model, which heats water as needed so that it won't waste energy sitting in the tank. If you live in a dry area like the southwest, consider purchasing an evaporative cooler instead of a traditional air conditioner; it will use less electricity. Look for the Energy Star label on new heating and cooling units.
If you're renovating your home, consider tapping into renewable energy sources. Solar panels, which have become sleeker over the years, are the most obvious way to recover energy in sunnier parts of the country (they feed electricity directly into the main grid, reducing the overall bill).
You might also consider a geothermal heat pump. In the winter, it uses a refrigerant and series of underground pipes filled with water to pull stored heat from the earth into your house. In warmer months, it sucks heat back out of your house. An added advantage of a geothermal pump is that certain models will also act as a hot-water heater.
Residential wind turbines are another interesting source of alternative energy to consider. Federal and state incentives and credits are available for many of these options. Visit the American Council for an Energy-Efficient Economy for a state-by-state summary and federal information.