You go to turn on the heat and your house just isn't getting warm like it used to. That furnace has been in the house longer than you have, so it looks like it is time to replace it. Buying a new furnace is a big investment, but there are ways to save some money, both now and in the long run. First, you need to decide between a singe-stage or two-stage furnace. A traditional single-stage furnace runs the burner at full blast and shuts off until heat is called for. It costs $500 less than a two-stage furnace, but the trade-off is lower energy efficiency, hot and cold spots, and inconsistent temperatures. A two-stage furnace has a high and a low burner setting. It normally runs on low unless full blast is needed. It costs $500 more than a single-stage unit, but it delivers consistent heat, which means fewer drafts and temperature swings, and is quiet and energy efficient. Another way to save money is to find out the right size of furnace for your home. You may actually need a smaller...