How many watts does a furnace use
While a furnace runs, it uses 800 W, and starting it takes 1,600 W for one second. The smallest portable unit that can run it has 2,000 W.
800 Wrunning, top of range
1,600 Wstarting surge
2,000 Wsmallest generator that runs it
Watts for running and starting
| Load | Running | Starting |
|---|---|---|
| Furnace blower | 800 W | 1,600 W |
Source: Champion wattage chart for a furnace fan. The nameplate on your furnace lists its exact rating in watts or in amps. To work out watts, multiply amps by 120 V. Use 240 V only when a two-pole breaker carries the load. A well pump is one example.
Smallest generator able to start it
A generator has to handle 800 W, which is 80% of its rating or less. It also needs to supply 1,600 W to start the furnace. The smallest portable size in common use, 2,000 W, handles both with room to spare. The same generator also takes on the running watts from any other load.