Noah Buhayar is a fellow at Rocky Mountain Institute.

If you live in a temperate or cold region of the United States, chances are you've fired up your home or apartment's heating system recently. The seasons change, the nights get a little colder. You flip the switch on your thermostat from "A/C" or "Off" to "Heat."

What's the net effect of everyone making that switch?

Most American households-more than 60 million-heat with natural gas. Another 32 million heat with electricity, 7.8 million with fuel oil, and 5 million with propane. Consuming those fossil fuels equates to roughly 7 percent of total U.S. greenhouse gas emissions, and about one-third of all residential greenhouse gas emissions.  

Then there's the cost. The average household in the United States spends about $889 per year on space heating. In particularly cold regions like the Northeast, annual home heating bills can reach $1,100 or more for natural gas or $1,800 for propane.

Saving emissions, and money, can be accomplished in two ways. One is "passive" improvements-measures you take to preserve the heat in your home. The other is to invest in a more efficient system for generating the heat in the first place.

Losing heat
Heat naturally flows from warmer spaces to cooler ones until the temperatures are equal.

Inside a home, warm air rises and leaks out the attic and roof while drawing cold air in through the basement.

Your home's shell (the walls, windows, doors, foundation, roof, attic, etc.) determines its rate of heat loss. Leaky shells can be responsible for 25-40 percent of the load on your heating system.

You can prevent this heat loss by improving insulation, sealing leaks, and replacing or reglazing your windows to minimize heat transfer. For more information, check out RMI's Home Energy Brief No. 1: Building Envelope.

Making your heating system more efficient
In addition to these measures, there are a number of steps you can take to improve the efficiency of your heating system.

• If you don't have one already, consider installing a programmable thermostat. These cost around $30-100 and allow you to preset a heating and cooling schedule that maintains a comfortable temperature when you're home, but lightens the load when you're not. Energy Star rates many such thermostats.

• If you have a furnace, seal your system's ducts with mastic and insulate hot-air ducts that pass through unheated spaces with fiberglass. Leaky ducts can decrease a furnace's efficiency by 20-30 percent.

• Most new boilers and furnaces come equipped with an electronic ignition for your pilot light. If your furnace or boiler doesn't have one (and you can turn your pilot light on and off safely), consider turning your pilot light off during the summer months when your heater's off.

You can find more tips about maintaining your home heating system at Energy Star's heating and cooling efficiency webpage.

Replacing your heating system
Want to do more? If your furnace is older than 10-15 years or your boiler is older than 20 years, then a new heating system will be at least 30 percent more efficient and will pay for itself in 5-10 years.

The American Council for an Energy-Efficient Economy has detailed information to help you determine whether to replace your furnace or boiler, find a good contractor, size your heating system, and calculate your return on investment.

If your annual heating and cooling costs are astronomical, consider augmenting your heating system's capabilities with in-space heaters or looking into a few new technologies like heat pumps and active solar heating.

You can find out more about both in RMI's Home Energy Brief No. 4: Space Heating.