A generator of 7,200 to 15,000 watts, or 7.2kW to 15kW, is needed to run a heat pump.
HVAC contractors recommend generators of 7.5kW to 20kW for heat pumps to make sure there is enough power to run the heat pump and other necessities like lights and the refrigerator.
It always makes sense to have too much power over not enough power.
Starting or Surge Watts: The reason you need such a large generator to run a heat pump is that it must supply both starting watts and running watts. The power required to start a heat pump is 3-5 times more than watts needed to keep it running.
Tip: The minimum generator size is determined by multiplying the amps needed for the circuit times the voltage of the heat pump.
So, if your unit requires a 30-amp breaker and uses 240 volts, which most central heat pumps do, then the minimum generator size is 7,200 watts.
What Size Generator for a 1.5 to 5 Ton Heat Pump?
The larger the heat pump, the more watts it needs to start and run. In any size heat pump, the more efficient it is, the fewer watts it requires. But the difference is small.
Generator size for 1.5 – 5 ton heat pump:
| Heat Pump Capacity | Generator Size |
| 1.5 Ton | 7,200 Watts / 7.2kW |
| 2 Ton | 8,000 watts / 8kW |
| 2.5 Ton | 10,000 watts / 10kW |
| 3 Ton | 12,000 watts / 12kW |
| 3.5 Ton | 14,000 watts / 14kW |
| 4 Ton | 16,000 watts / 16kW |
| 5 Ton | 20,000 watts / 20kW |
What size generator for 3 ton heat pump?
A 12,000 watt generator is recommended for a 3 ton heat pump. That’s 12kW.
A generator as small as 8,000 watts (8kW) might be enough to start and run a 3 ton heat pump, but you would have very little power left to run anything else.
Portable generator vs backup generator: Only the largest portable generator units have enough juice to run a central heat pump.
If you’re shopping for a generator to run a heat pump, your best choice is a whole-house generator, also called a backup generator, stationary generator and standby generator.
They should be wired directly to the electrical panel, and with the flip of a switch (some switch over automatically), your heat pump will be up-and-running.
Will a 20kW generator run a heat pump?
Yes, a 20kW generator will run a heat pump of any size up to 5 tons. And that’s the largest heat pump size for residential use.
With a 20kW, or 20,000 watt generator, you should have enough power to run the heat pump, a refrigerator, some lights and a few other essentials.
Will a 12000 watt generator run a heat pump?
Yes, a 12000 watt generator will run a heat pump up to about 3 tons.
If you don’t run anything else off the generator, it might run a heat pump as large as 4 tons.
But as noted earlier, it makes sense to buy a larger generator. In a power outage, you’ll want as much energy as possible to run your heat pump and other vital components of your home.
Will a portable generator run a heat pump?
No. Most portable generators will not run a heat pump. Only the largest have enough power to start and run a small central heat pump, like a 1.5 ton or 2 ton unit.
Does it matter if the heat pump is heating or cooling?
No. A heat pump requires the same amount of power whether it is in Heat mode or AC mode.
The one exception would be if it is in Heat mode and it is relying on auxiliary heat (Aux) or emergency heat (EM). These modes utilize the 5kW to 20kW heat coils in the air handler.
Depending on what else the generator is powering, it might not have enough juice for the electric heat coils.
More tips – The Howell-Oregon Electric Cooperative provides other good tips for using a standby generator to run your heat pump and other household appliances and lighting.
Safety tips and tips for choosing the right size generator are included.
