Cut prewar home's energy bill

Replace old furnace, ductwork with high-efficiency unit

Talk about misplaced priorities: In the name of saving energy, many people think nothing of spending tens of thousands of dollars on replacement windows. But at the same time, they’ll willingly limp along with an obsolete furnace whose replacement would have a far greater payoff, dollar for dollar, on both their utility bills and their home’s comfort.

The bottom line is that, if improving your home’s energy efficiency is the main goal, replacing your windows is among the least cost-effective ways to do it. Here’s why: Although glass radiates heat at a substantially higher rate than walls or ceilings do, it represents only a small fraction of a home’s exterior surface area.

A typical 1,800-square-foot, one-story rancher, for example, will have a window area comprising something on the order of just 6 percent of the exterior envelope. In the same house, however, the ceilings represent a whopping one-third of the surface area.

Therefore, the most cost-effective way to improve energy efficiency in homes built before the 1980s is simply to increase attic insulation levels.