How It Works

A gas-fired furnace produces hot air to heat a home through an air duct system. Gas-fired boilers - also called gas furnaces - produce hot water or steam for a baseboard or radiator heating system and for general hot water use. Both systems use either a natural gas line or a propane tank. They use a combustion system consisting of a blower, fuel supply, ignition system (or pilot light) and a control system.

What Can Go Wrong?

A furnace has many components that can fail, most of which can be repaired by maintaining or replacing individual pieces. For example, the burner or blower motor can fail and need replacement, or components in the control system can fail. Replacement is usually required when a combustion chamber fails in a hot air furnace or when water leaks in a boiler system.

Environmental Impact

Heating is the largest energy expense in most homes, accounting for 35 to 50 percent of annual energy bills in colder parts of the country. Gas-fired home furnaces range in size from 13.2 kilowatts (kW) to 88 kW. The average home using gas consumes 49,000 cubic feet of gas per year for space heating, producing approximately 5,733 pounds of carbon dioxide (CO₂). 

Gas-fired furnaces and boilers are major energy consumers and sources of CO₂ in the home. Gas furnaces are ranked according to their annual fuel utilization efficiency (AFUE) which is a representation of the energy efficiency of the furnace during the heating season. It can range from 65 percent in older units to 97 percent in newer ones. When replacing the furnace, the higher the AFUE, the lower the energy usage, energy cost and CO₂ footprint.