What size power station runs a gas furnace?
Your gas still flows in a blackout, but the furnace won't run without electricity. Here's what it draws, how much battery that takes, and the one part you shouldn't do yourself.
Why a gas furnace stops in an outage
A modern gas furnace needs electricity for its electronic igniter, control board, safety controls, draft-inducer fan and the blower that pushes warm air through the ducts. Lose power and it stops, even with a full gas supply. Older standing-pilot furnaces may still light, but the blower won't run. The blower is the big electrical load, so it's what you size for.
How many watts it takes
| 1/3 HP furnace fan | 700 W running, 1,400 W starting (Honda) |
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| 1/2 HP furnace fan | 875 W running, 2,350 W starting (Honda) |
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These are conservative chart values from a generator maker. The rating plate inside your furnace's blower door is better, and variable-speed ECM blowers often draw well below them. The blower also cycles: it runs when the thermostat calls for heat, which depends on outdoor temperature and insulation. That's why the planner below asks for a duty cycle.
Furnace runtime planner
What the example shows
A 1/3 HP blower at Honda's 700 W running half the time for 12 hours needs 4,200 Wh, or about 5,250 Wh with our buffer (the planner shows a bit more because it includes the router). That's beyond most 1 to 2 kWh portable units and points to expandable home-backup units like the EcoFlow DELTA Pro 3 with an extra battery (or another expandable unit with an add-on battery; the 5,040 Wh Jackery Explorer 5000 Plus lands just short of this example on its own) or a plan that adds solar or generator recharging. If your blower is a lower-draw ECM motor, the numbers fall a lot, so measure or read the nameplate first.
Connecting it: hire a licensed electrician
Most furnaces are hard-wired, with no plug. Powering one from a power station takes a transfer switch, inlet box, or a maker's home panel (for example EcoFlow's Smart Home Panel 2) installed by a licensed electrician. Don't build or use a "suicide cord" or backfeed an outlet: it can electrocute utility workers and start fires. StationSizer doesn't give wiring instructions.
Cold-weather notes
- Lithium power stations have charging temperature limits. EcoFlow lists 32°F to 113°F for charging the DELTA Pro 3, and Anker lists 32°F to 104°F for the C1000 Gen 2. Keep the unit in a heated or above-freezing space if you plan to recharge it.
- Keep battery-operated CO alarms on every level. Your furnace still burns gas, and any backup generator is a CO source (CPSC).
FAQ
Does a gas furnace work when the power is out?
Usually not. A modern gas furnace uses electricity for its igniter, control board, inducer fan and blower, so it shuts down without power even though the gas supply is fine.
How many watts does a furnace blower use?
Honda's generator wattage guide lists a 1/3 HP furnace fan at 700 running and 1,400 starting watts, and a 1/2 HP fan at 875 running and 2,350 starting watts. Newer variable-speed (ECM) blowers often draw less, so the nameplate on your unit is the best number.
Can I plug my furnace into a power station?
Only if the furnace has a factory cord and plug, which most don't. Most furnaces are hard-wired, and connecting one to a power station needs a transfer switch, inlet or panel installed by a licensed electrician. Never improvise a connection or backfeed an outlet.