Big running load, moderate surge
A 10,000 BTU window unit is one of the biggest running loads you can plug in, and its compressor still needs extra power to start. In most outage lists it pushes up the running watts more than the starting watts — which is exactly why letting it take turns pays off.
Letting the AC take turns with other big loads — microwave, coffee maker, hair dryer — often drops you a whole generator class.
Window AC plus the rest of the house
Motors don’t all start in the same second, so you only add the single biggest startup jump on top of everything that’s running.
- Window AC + fridge + sump pump: 2,950 W running, 5,150 W starting → at least 3,688 W rated (mid portable). Open in calculator
- Same, plus a microwave running together with the AC: 3,950 W running, 6,150 W starting → at least 4,938 W rated (mid portable). Open in calculator
- Same, with the AC and microwave taking turns (the microwave adds nothing): 2,950 W running, 5,150 W starting → at least 3,688 W rated (mid portable). Open in calculator
We divide the running load by 0.8 because a generator shouldn’t sit above about 80% of its rating for hours.
Questions
Does a bigger window AC need a much bigger generator?
Yes — both running and starting watts grow with BTUs. Use the calculator’s custom appliance with the numbers from your unit’s label.
Can a soft starter help?
Soft-start kits lower a compressor’s startup surge. Check that one is made for your model.