A gas furnace needs electricity for its blower and controls. Learn safe ways to power it in an outage, including transfer switch and CO rules.
- A gas furnace still needs electricity for its blower and controls, so no power usually means no heat.
- Connect a battery or generator only through a setup installed by a licensed electrician, never by backfeeding.
- Generators and fuel-burning heaters stay outdoors or are never used inside; keep working CO alarms in the home.
Many people assume a gas furnace will keep working when the power goes out because the fuel is gas. In most homes it will not. The burner needs gas, but the control board, ignition, safety sensors and blower fan all need electricity. No power usually means no heat, even when the gas is still flowing.
The good news is that a furnace can often be powered through an outage. The bad news is that the wrong way to do it can start a fire, shock a utility worker or cause carbon monoxide poisoning. This guide explains the safe routes.
What a gas furnace actually draws
A modern gas furnace uses far less electricity than an electric heater. Look at the furnace nameplate or manual for its amps and voltage. Multiply them to get watts. A typical blower motor and controls use a few hundred watts while running, though models differ, and a start-up surge is higher. Variable-speed fans tend to draw less. Oil furnaces and some boilers have their own pumps and igniters with similar needs.
Two things matter before you plan anything. First, check the label for the figures, not an internet average. Second, confirm the furnace type: electric furnaces and heat pumps with electric resistance heat draw thousands of watts, which is beyond what most portable batteries can sustain.
Option 1: Power station through a licensed electrician
Most furnaces are hardwired, which means there is no plug to push into a power station. Some installers add a dedicated outlet or a small inlet so a battery or generator can feed the furnace circuit. This work should be done by a licensed electrician and may need a permit, depending on where you live. It must isolate the home from the utility grid so power cannot flow back out.
- Ask for a setup that powers only the furnace circuit, not the whole panel.
- Check that the battery can handle the furnace's surge as well as its running watts.
- Estimate runtime: capacity in watt-hours divided by average watts. Furnaces cycle on and off, so the average is lower than the running figure.
See what size power station do I need for the sizing approach.
Option 2: Portable generator with a transfer switch
A portable generator can run a furnace for as long as you have fuel. The safe way to connect is a transfer switch or an interlock kit with a proper inlet, installed by a licensed electrician. Our guide on transfer switches vs extension cords explains the difference.
Never plug a generator into a wall outlet using a cord with two male ends. This is called backfeeding. It can electrocute line workers repairing the grid and can start fires in your wiring.
Carbon monoxide safety
Carbon monoxide (CO) is the biggest hazard in winter outages. It comes from generators, fuel-burning heaters, grills, camp stoves and vehicles running in enclosed spaces. Official guidance in both Canada and the US is the same: never use these devices indoors or in attached garages.
- Install CO alarms on every level and near sleeping areas. Use battery-powered or battery-backup models.
- Check that the furnace vent and the outdoor intake or exhaust are clear of snow and ice.
- If an alarm sounds or you feel dizzy, nauseous or have a headache, get everyone outside to fresh air and call emergency services.
If you cannot power the furnace
Have a plan B. Close off rooms you do not need, shut curtains, and gather in one small room. Put towels along door gaps, wear layers and use sleeping bags. Our guide on how to stay warm without power covers this in detail. Only use heaters that are rated for indoor use and follow the manual, and never use a barbecue, camp stove or oven to heat a home.
If the house cools down, shut off the main water supply and drain pipes if you are leaving, or let taps drip slightly if you are staying. Ask a plumber for local advice on freeze protection.
Before the next winter
- Read your furnace label and note the running and starting watts.
- Ask an electrician what a safe connection would cost and whether a permit is needed.
- Test your CO alarms and replace batteries.
- Store fuel safely and rotate it.
- Review our winter storm prep checklist and the heat and light hub.
Quick answers
Can I plug my furnace into a portable power station?
Only if it is a plug-in model or an electrician has added a safe inlet or outlet. Most furnaces are hardwired, so do not splice or modify wiring yourself.
Is it safe to use an oven or barbecue for heat?
No. Ovens, grills and camp stoves are not designed to heat homes and can produce carbon monoxide. Use only equipment rated for indoor use, following the manual.