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 - WEN 56360iX
3,600W starting · 53% headroom · $609.23
Comfortable headroom without overpaying for capacity, has a CO shutoff sensor.
Check price - Generac iQ3500
3,500W starting · 49% headroom · $1,049
Comfortable headroom without overpaying for capacity, has a CO shutoff sensor.
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