Power outages during the winter are serious concerns. Unless you have a wood fireplace, having the electricity go out means you won’t be able to heat your home until the power is restored. While gas furnaces produce heat by burning natural gas, they also use a small amount of electricity to power certain components. For instance, modern gas furnaces use either a hot-surface igniter or an intermittent pilot to light the burners, both of which require electricity to turn on. Even old furnaces with a standing pilot light require electricity. The thermocouple is a safety mechanism that ensures gas doesn’t continue to flow to the pilot light if the flame goes out, and it uses a small electrical current to detect the flame. Without electricity, the gas to the pilot will shut off and the flame will go out, preventing the burners from igniting.
How a Gas Furnace Works
Gas furnaces produce extreme amounts of heat, making them reliable and effective options for heating homes in cold climates. For a gas furnace to turn on, numerous components have to work in tandem.
The process starts with the thermostat sensing the temperature and sending a signal to the furnace control board when the temperature drops below the set point. The control board then signals the draft inducer to turn on. The inducer is a small fan that draws air upward through the furnace and creates negative air pressure within the unit, which serves two purposes. The first is that it draws air into the combustion chamber, ensuring the flames receive sufficient oxygen. The inducer also draws the hot combustion fumes up through the heat exchanger, which ensures the furnace heats effectively and that the fumes get safely vented outside.
The negative pressure created by the draft inducer activates a component known as the pressure switch. This signals the control board to open the gas valve and turn on the electronic igniter. Another component, known as the temperature limit switch, monitors the temperature of the heat exchanger. When it senses that the exchanger is sufficiently hot, it signals the control board to turn on the blower motor. The blower then starts drawing air into the furnace. The heat radiating off the exchanger quickly heats the incoming air to between 130 and 170 degrees Fahrenheit. The blower then circulates the heated air into every room through the supply ducts.
Once the thermostat senses that the right temperature has been reached, it signals the control board to turn the furnace off. The blower continues to run for a few minutes to take advantage of all of the latent heat remaining in the heat exchanger. Once the limit switch senses that the heat exchanger has cooled past a set point, it will signal the control board to switch the blower off.
What Do Gas Furnaces Use Electricity For?
The majority of the process we just explained requires electricity. The thermostat sends a low-voltage electrical current to the control board to signal the furnace to turn on and off. Low-voltage signals also get sent back and forth between the control board and various other components. For instance, when the pressure switch activates, it closes an electrical circuit so that a signal gets sent back to the control board. The control board then sends a current to open the gas valve. Other components, like the flame sensor, blower, draft inducer, limit switch, and flame rollout sensor, also require electricity to work.
Gas furnaces use the most electricity during the initial start-up due to the electronic igniter coming on and the control board opening the gas valve. Once everything is running, the blower is by far the biggest source of electricity consumption. The second biggest source is the draft inducer because it also runs continuously throughout each heating cycle.
How Much Electricity Do Gas Furnaces Use?
The size and type of the furnace are the main factors that determine how much electricity it uses. The age of the furnace can also play a role since many older furnaces have inefficient blowers that have higher energy demands than modern blowers.
Most furnaces use between 300 and 1,200 watts of electricity per hour. In colder climates, a gas furnace typically runs for around a total of eight hours per day on average. That means it would use somewhere between 2,400 and 9,600 watts of electricity on a normal day.
Larger furnaces consume the most electricity, as they require larger, more powerful blower motors. Variable-speed furnaces have the lowest electricity requirements. These furnaces have a variable-speed blower that continually adjusts how quickly it runs and how much air it circulates based on the current heating demand. Some variable-speed blower motors can slow down to the point where they only consume around 75 watts per hour.
How Gas Furnaces Compare to Fully Electric Furnaces
Whereas gas furnaces produce heat through combustion, electric furnaces have resistance heating coils that convert electricity into heat. When the furnace turns on, electricity begins flowing through the coils. The resistance the current encounters as it flows through the coils causes the metal to almost instantly start glowing and becoming red hot. The easiest way to understand this process is to think about how the wires inside a toaster start glowing and giving off heat as soon as you turn it on.
As with gas furnaces, electric furnaces use a blower to draw cooler air in and circulate heated air around the house. The blower in an electric furnace is no different than that in a gas furnace, and both have about the same electricity demand. Nonetheless, electric furnaces consume far more electricity overall. Even a small electric furnace that only produces 34,000 BTUs of heat consumes 10,000 watts of electricity in just a single hour. The largest residential electric furnaces available produce 68,000 BTUs of heating and consume a whopping 20,000 watts of electricity.
On the face of things, trying to compare the overall energy demands of gas and electric furnaces can seem like comparing apples to oranges. After all, you need to consider both the amount of gas and the amount of electricity a gas furnace uses. Comparing the energy usage and operating costs isn’t that difficult. The fact is that gas furnaces use far less energy overall than electric furnaces.
The amount of electricity it requires to run electric furnaces means they’re mostly just suitable for places with warm winters where you don’t need a big furnace and don’t need to heat your house all that often. Trying to heat a house in a cold climate with an electric furnace can be extremely expensive and will often cost double what you’d pay to run a gas furnace.
IBBOTSON Heating & Air Conditioning Co. is a family-owned and -operated company that’s been providing honest, dependable heating and cooling services in Arlington Heights and throughout the Northwest Chicago suburbs for nearly 80 years. We’re a Lennox Premier Dealer and a Carrier Factory Authorized Dealer, and we offer some of the best furnaces and other HVAC equipment you can find. Whether you want to upgrade to a new furnace or need to schedule maintenance or a furnace repair call, contact us for service and support you can trust.
