What size generator to run a window ac (12k btu)?
Window AC (12k BTU) sizing at a glance: it draws 1300 running watts, surging to 3380W at startup.
| Spec | Value |
|---|---|
| Running watts | 1300W |
| Starting (surge) watts | 3380W |
| Recommended class (this load + margin) | 4500W |
Why the startup surge matters
Because a window ac (12k btu) has a motor, it surges to about 3380W at startup — roughly 2.6× its running draw. If you size a generator only for the running watts, it can stall the instant the window ac (12k btu) switches on. Always size for the surge.
Sizing the whole system
The number above covers the window ac (12k btu) on its own with a safety margin. In a real outage you'll run other things too — and the right method is your total running load plus the single largest surge among everything, not the sum of every surge. Use the full calculator to size your actual setup:
Common questions
How many watts does a window ac (12k btu) use?
A typical window ac (12k btu) draws about 1300 running watts, but needs roughly 3380 watts at startup due to motor surge.
What size generator runs a window ac (12k btu)?
For the window ac (12k btu) alone plus a safety margin, a 4500W (≈4.5kW) class generator is appropriate. Add your other essential loads to size the full system.