What size generator to run a furnace blower?
Furnace blower (gas) draws about 800W while running and surges to 2,350W on startup. Allowing 20% headroom, size for at least 2,900W of starting capacity.
A gas furnace needs only its blower and controls powered — this is why modest generators keep a house warm.
The surge is the number that matters. A generator rated to 800W will stall the moment the motor kicks in, because for a fraction of a second it needs 2,350W. Manufacturers advertise running watts, which is why people routinely buy one size too small.
Units that cover it
- Predator 3500 Watt Super Quiet Inverter
3,500W starting · 49% headroom · $799.99
Comfortable headroom without overpaying for capacity, has a CO shutoff sensor, runs at 56 dB.
Check price - Honda EU3000iS
3,000W starting · 28% headroom
Comfortable headroom without overpaying for capacity, has a CO shutoff sensor, runs at 57 dB.
Check price - Honda EU3200i
3,200W starting · 36% headroom
Comfortable headroom without overpaying for capacity, has a CO shutoff sensor, runs at 58 dB.
Check price
Running more than one thing
Most people are not powering one appliance. Add everything you need at once and the calculator works out the real peak — your total running load plus the single largest surge, not the sum of every surge.
Size the whole load