Where can thermal energy be lost?

Thermal energy can escape from a home in several ways. Every time heat escapes through an open or poorly sealed door or window, thermal energy is lost. It passes right through window glass as well, especially single-glazed windows. Doors and windows are the most common and visible culprits in thermal energy loss, although poorly insulated walls, ceilings and heating ducts are other sneaky contributors.

Thermal energy in the hot water supply is lost through uninsulated pipes or water tanks. Thermal energy can even be lost if it never makes it to the outdoors. If a couch or other piece of furniture is placed over a heating vent, thermal energy can be wasted as well - effectively heating the couch but not the living space. The failure to capture passive solar thermal energy when it is available could also be counted as thermal energy loss. Sunlight offers valuable solar heat through windows, but when blinds or drapes are left closed on a sunny winter day, that free heat is trapped at or outside the window.

No heating system is perfect. Electric, gas and even solar space and water heaters do not deliver 100 percent of the heat created or collected by the system to the home. The difference is that solar thermal systems utilize free solar radiation, while conventional systems are wasting thermal energy pulled from electric cables or gas lines. A significant portion of thermal energy in forced-air heating systems is simply lost through venting, though heat recovery ventilators can recapture much of that energy.

Thermal energy is all around us and affects our lives in so many ways. When you're boiling water in a pot smaller than the burner, for example, thermal energy is also lost. When you walk outside in winter improperly dressed for the weather conditions, you sacrifice some of your body's own thermal energy. When you let the shower run for 10 minutes before climbing in, thermal energy used to heat that water is lost. Indeed, thermal energy conservation is at the heart of energy efficiency. Increasingly, new homes are built to have a tight thermal seal, including tight insulation, improved weatherstripping around doors and windows, thermal walls, extensive caulking, house wrap, cool roofs and more - all in the name of minimizing thermal energy loss.