Cost: Anywhere from $3,000 to $10,000 for an energy-efficient model.
Advantage: 85 percent to 95 percent efficient; tax rebate of up to 15 percent of the cost of the furnace if it's Energy-Star rated.
"Insulation
pays you back every time your furnace doesn’t come on," says Barrows. "Getting a highly energy-efficient furnace pays you back every time it does come on."
A traditional furnace can lose up to half its heat through leaks in its pipes, says Spofford. The same is true for leaking air-conditioning ducts. If your furnace or AC unit is decades old, the loss likely is greater.
An energy-efficient furnace, by contrast, only loses 5 percent to 12 percent of the heat it generates. And if you insulate your house well, you can buy a smaller one, says Barrows. Have your contractor run a Manual-J assessment. It's the most widely used software program among building professionals and calculates how much heat your house will need. That, in turn, will allow you to buy a furnace just large enough for your needs.
You'll also find that an energy-efficient furnace or air-conditioning unit will pay for itself in four to seven years, says Barrows -- not bad if you plan to be there for 20.