Will a generator run a mini split?

Mini splits are some of the easiest air conditioners for a generator to run, once you get the voltage right. Search results on this topic often disagree, so here's the plain version.

How many watts does a mini split use?

We worked this out from ENERGY STAR's data on nearly 17,700 certified mini-split heat pumps. Each listing gives the cooling capacity and the EER2, which is the efficiency at full cooling on a hot (95°F) day. Capacity ÷ EER2 = watts at full cooling.

Mini split size	Typical watts at full cooling	Most models fall between
9,000 BTU	about 670 W	560–750 W
12,000 BTU	about 920 W	860–1,000 W
18,000 BTU	about 1,440 W	1,300–1,540 W
24,000 BTU	about 1,960 W	1,800–2,180 W

Most of the time a mini split runs well below this, because it slows down once the room is cool. Our calculator uses 1,000 running watts for a 12,000 BTU unit.

What about starting watts?

This is where mini splits shine. Most modern ones use an inverter compressor, which ramps up slowly instead of slamming on like a window AC. So the start-up surge is small. Our calculator uses 1,200 starting watts for a 12,000 BTU unit. That's our estimate, not a published figure, so check your model's manual.

Older or budget "fixed-speed" mini splits are different. They can surge like a window AC, at two to three times their running watts.

The real catch: 120 V or 240 V?

Many mini splits, especially 18,000 BTU and up, run on 240 V. Some 9,000 and 12,000 BTU models run on 115 V. Check yours:

• Look at the outdoor unit's label. It lists volts, amps and often "max input" watts.
• Look at the breaker. A double breaker (two handles tied together) means 240 V.
• Check the manual or the spec sheet under "power supply."

If it's 240 V

A 240 V mini split can't run from the generator's normal 120 V outlets. You need:

1. A generator with a 240 V outlet, usually the 4-prong L14-30. It's rated 30 A at 120/240 V, or 7,200 watts.
2. A transfer switch or interlock installed by a licensed electrician, so the generator can feed the mini split's circuit.

Never backfeed the house through a dryer outlet or wall outlet. It can electrocute a utility worker and start a fire. See interlock vs transfer switch.

If it's 115 V

A 115 V mini split is simpler. A 2,000–3,000 W inverter generator can usually run a 9,000–12,000 BTU unit. Most are hard-wired with no plug, so it still needs a transfer switch or interlock to connect safely.

A worked example: 12,000 BTU mini split and a fridge

• Running: 1,000 (mini split) + 400 (fridge) = 1,400 W
• Biggest surge: the fridge, 1,200 − 400 = 800 W
• Starting: 1,400 + 800 = 2,200 W
• With 20% headroom: about 1,700 running and 2,650 starting watts

A 3,000 W class generator covers this, if it has the right voltage. The calculator above is set up with this pair and will flag the 240 V need.

Will a 3,500 watt generator run a mini split?

Yes on watts, for one 9,000–18,000 BTU unit. The question is whether it has a 240 V outlet if your unit needs one. See what a 3,500 watt generator can run.

Why an inverter generator is the safer pick

A mini split is full of electronics: the inverter board that drives the compressor, and the fan controls. Clean, steady power is kinder to them. Generators list total harmonic distortion (THD), where lower is cleaner. Westinghouse's manuals show the gap: 23% or less on an open-frame model and 3% or less on an inverter model.

Some mini splits also have a setting that limits how much power they draw, for use on generators. People search for it as "generator mode." If your manual lists one, use it.

Two mini splits, or a multi-zone system?

Add them up. Two 12,000 BTU heads on separate outdoor units need about 2,000 running watts together. Their inverter compressors ramp up slowly, so the start-up surge stays small. A multi-zone system with one big outdoor unit is sized by that outdoor unit: a 24,000 BTU unit draws about 1,960 W at full cooling. Either way, 240 V is likely.

Heating in winter

A heat pump mini split can keep heating in an outage too. In very cold weather it works harder, and it may switch on built-in backup heat if it has any. Check the outdoor unit's label for its maximum input watts or amps, and size to that, not the typical number.

Check your own mini split

1. Read the outdoor unit's label for volts, rated amps and max amps.
2. Multiply max amps by volts for the most it can draw. A 240 V unit with 5 max amps can draw about 1,200 W.
3. Add your other loads in the calculator above.

Safety: Run it outdoors only, 20+ feet from the house, away from windows and doors. Read our carbon monoxide guide.