How they work

Both gas and electric furnaces work using a forced air heating system. The first piece of equipment used in both furnaces is the thermostat ². When the temperature in the room falls below the heat set point on the thermostat, a signal is sent to the furnace unit.

In the case of a gas unit, the signal will cause the pilot light to ignite the main burner of the heat exchanger. The pilot light is a small flame that is always burning. The heat exchanger draws heat from the main burner and heats the air that will circulate to the house. By contrast, in an electric furnace, an electric ignition receives the thermostat signal and activates electric heating elements inside the furnace.

In both types of furnaces, heated air is forced by a blower fan through the ductwork into the various heated rooms of the house. Cooler air is drawn through an intake vent to return to the furnace. When the desired temperature is sensed by the thermostat, the furnaces shut off their heating elements. The fan dissipates the remaining heated air and shuts off as well.

Heat and Energy Efficiency

An electric furnace is the more efficient of the two. It may have an annual fuel-utilization-efficiency (AFUE) rating as high as 100 percent. Gas furnace ratings range from 55 to 97 percent. The greatest factors in the variation are the type of unit chosen and the amount of heat lost through a gas furnace’s flue or other areas.

Energy efficiency only means the amount of energy that the furnace turns into heat - not the rate at which it heats your home. Electric furnaces convert nearly all of their energy into heat, while gas furnaces can vary. Gas furnaces generally heat homes more quickly than electric furnaces, despite lower efficiency.

Higher efficiency can be gained in a gas furnace with an alternative to the traditional pilot light such as an intermittent, direct spark, or hot surface ignition. The higher cost of a more efficient gas system will most often be offset by lower fuel costs in regions with harsh winters.

Additionally, a gas furnace will heat the home faster because the heat produced is hotter than the heat produced by electric coils. This and the cheaper cost of natural gas make gas heat a better option for colder climates. In a warmer climate with less demand for heating, an electric furnace with its lower initial cost and reduced maintenance needs may serve a homeowner better.

Maintenance and Safety

An electric furnace is easier to maintain and requires less professional attention. There is no burner to clean or inspect, and the system itself doesn’t generally require cleaning or care of any kind. This can make an electric furnace easier and less expensive to maintain over its lifetime.

A gas furnace, however, needs regular maintenance by an HVAC professional to keep it efficient and safe. The furnace should be cleaned and inspected yearly. It should be checked to make sure that the system is operating normally, and that no condensation is building up below it, as this can cause corrosion over time. As stated in the installation section, combustion heating gives off small amounts of carbon monoxide. Only an HVAC professional has the proper equipment and knowledge to ensure that all areas of the system are sealed and working properly. Improper maintenance and ventilation can result in carbon monoxide poisoning. All gas-burning appliances should be properly ventilated and maintained to lessen this risk. Homes with gas appliances should also be equipped with carbon monoxide detectors as an added precaution.

Noise

An electric furnace is generally quieter than a gas furnace. This is mostly due to the simplicity of the design; there are fewer moving parts, no vents and no burner. This makes for a quieter furnace overall. Gas furnaces are not necessarily noisy, but they do make a loud rushing sound at the time that they start up and the burner ignites.​