Only home standby generators can power heat pumps larger than 2 tons. However, even smaller heat pumps require expertise in wiring and setup.
In this article, we’re going to check the wattages, different heat pump sizes use, and which generators suit each heat pump size.
Quick answer: Only a home standby generator can power a medium-sized heat pump. Small heat pumps of 1-2 tons can be powered off large portable generators. However, getting a portable generator just for powering a heat pump is cost-inefficient. Rather, consider getting a wood stove or a propane heater. These provide more BTUs of heat energy for less money.
How much power do heat pumps use?
The power your heat pump uses depends on its size (in tons or BTUs) which directly correlates with the size of your home.
An average heat pump with a heating efficiency of 20 SEER consumes 600W per 1 ton.
However, the power of heat pumps ranges from 545W – 850W per ton depending on the SEER rating.
SEER stands for Seasonal Energy Efficiency Rating and determines the amount of BTUs a heat pump can move per Watt.
A SEER rating of 20, for example, says that a heat pump is able to move 20 BTUs of heat per Watt.
A high SEER rating is generally better than a lower one.
The upper power consumption limit of 857W per 1 ton (which equals 12,000 BTUs) stems from the minimum allowable SEER rating for heat pumps which is 14.
12,000 BTUs / 14 SEER = 857.14W
This upper power consumption limit is valuable for finding out the generator size we need. All heat pumps are legally required to consume less than 857.14W of power per ton.
You can find out the exact heat pump size you need through a house audit performed by a professional. They will set up a door construction (or “blower door test”) that measures your house’s heating needs.
“This blower door test, combined with some other data, like the climate of the city you live in, will help them produce a Manual J Load Calculation, which is the industry standard way to size an HVAC system.”
Often these measurements are free of charge. Of course. The HVAC company wants to sell you a heat pump, so it lowers your entry barrier to buying from them.
Power consumption of different heat pump sizes
|House size (in square feet)||Heat pump size (in tons)||Maximum average power consumption (in Watts)|
|500 sq. ft.||1 ton||857W|
|1,000 sq. ft.||2 tons||1,714W|
|1,500 sq. ft.||3 tons||2,571W|
|2,000 sq. ft.||4 tons||3,429W|
|2,500 sq. ft.||5 tons||4,286W|
|3,000 sq. ft.||6 tons||5,143W|
Please note that the right column lists the maximum average power consumption. The maximum average power consumption is the maximum amount of power that a heat pump consumes on average. It is NOT the maximum power consumption.
The maximum average power consumption determines the power consumption for the worst legally allowable SEER rating of 14.
According to the table, you need about 1 ton per 500 square feet of house area.
How much power do generators provide?
Different size generators produce different amounts of power.
Here’s a table with the most common generator types, the amount of power they produce, and their respective prices.
|Small Recreational Generator||< 2,000W||$450 – $1600|
|Midsized Inverter||2,000W – 3,500W||$800 – $2,400|
|Large Portable Generator||< 8,500W||$950 – $2,000|
|Large Inverter||5,000W – 7,500W||$1,400 – $1,800|
|Home Standby||< 20,000W||$2,000 – $6,000|
Which size generator can run a heat pump?
Only a home standby generator can reliably run a heat pump. Smaller generators are theoretically able to power small 1-2 ton heat pumps. However, you can’t power additional appliances with them.
The amperage a heat pump needs to get started is 3x the amperage it needs once it’s running.
Respectively, for starting, a heat pump needs 3x the power. A generator should, therefore, be able to support 3x the power a heat pump is classified for.
Let’s have a look:
|Heat pump size (in tons)||Required startup power (in Watts)||Theoretical smallest generator required|
|1 ton||2571W||Midsized Inverter (2kW – 3.5kW)|
|2 tons||5143W||Large Inverter (5kW – 7.5kW)|
|3 tons||7714W||Home Standby (<20kW)|
|4 tons||10286W||Home Standby (<20kW)|
|5 tons||12857W||Home Standby (<20kW)|
|6 tons||15429W||Home Standby (<20kW)|
As you see, for most heat pump sizes a home standby generator is required.
Smaller 1-2 ton heat pumps may theoretically run off a midsized inverter or large inverter-type generator.
However, you should get a professional’s consultancy and confirmation on whether using anything else than a home standby generator in your case makes sense and is technically possible.
Another problem with using small generators is that you are not able to power any appliances aside from the heat pump.
In an energy outage, a heat pump is not a priority. Other devices, such as a fridge, are a lot more important because they keep you alive! A heat pump is only a luxury.
It is, therefore, pointless to size a generator exactly for one heat pump without accounting for additional buffer power.
Will a portable generator run a heat pump?
Regular portable generators are not able to power a heat pump. An extra strong portable generator might theoretically be able to power a heat pump. However, you should consult an expert to perform the wiring.
Can a portable generator power a mini split heat pump?
Mini split heat pumps are a smaller and almost portable form of heat pumps. An average mini split heat pump uses around 2,000W.
They are designed for regular wall-outlet use. Therefore, we don’t have to account for any wiring and startup issues as with regularly sized heat pumps.
Yes, a portable generator rated > 3,000W can reliably run an average 2,000W mini split heat pump. Place the generator outdoors. Otherwise, it mitigates the heat pump’s efficiency.
Also, a generator exhausts toxic gases such as carbon monoxide and carbon dioxide. You don’t want them in your living space.
Does powering a heat pump off a generator make sense?
Powering a heat pump off a generator is only worth it for long-term usage. Buying a generator to power your heat pump, or buying a heat pump to run off your generator, just to cover emergency situations does not make sense.
Both a heat pump and a generator are very expensive appliances. Additionally, they require maintenance.
Both heat pumps and generators contain moving parts, which cause friction and wear down. Heat pumps and generators are very prone to wear and tear.
For emergencies, it is better to use low-maintenance and cost-effective heating methods for energy outages.
Two of the best heating methods that don’t require electricity and that don’t need any moving parts are
- wood-burning stoves and
- propane gas heaters
If you are thinking about buying a heat pump or a generator (if you don’t have these yet), then please consider getting a wood stove first!
Wood stoves produce by far the most BTUs of heating energy per dollar spent. They are the objectively most cost-effective heating method.
Additionally, you can stack and store a lot of wood in your garden. It is much harder to store a lot of fuel for powering a generator. It might even be legally prohibited in your location.
If you now think that both wood-burning stoves and heat pumps are too expensive, then I highly recommend getting a propane gas heater, such as this Mr. Heater Big Buddy.
It produces as much heat energy as a wood stove and even more than a small heat pump!
However, with about $150 (or <$100 for smaller models), it costs just a fraction of a heat pump or a wood stove.
You’ll only need to store some propane gas at home. A 20-lb tank costs about $15 and lasts you for weeks if you use it economically.
How to install a generator with a heat pump?
To install a heat pump and connect it to a home standby generator, you have to hire a licensed electrician.
Several issues make heat pump installation with generators hard:
- Complicated wiring. Some heat pumps run on two different input voltages (120V and 240V which needs to be accounted for)
- Asynchronous frequencies. Starting a generator that is not in sync with your neighborhood’s electric grid can be a safety issue and cause lethal shocks
- Lack of resources. There are no proper resources online on how to do it for a reason. Only licensed electricians are qualified to do it
- Interference with neighbors. It might be necessary to check and understand the neighbor’s power supply, especially if they also have a home standby generator
Personally, I don’t recommend being the person responsible for accounting for and solving these issues. If something goes wrong, your insurance (if you even have one), won’t be happy. And probably they won’t take responsibility for your carelessness.
You can run a heat pump off a home standby generator. However, you will need a licensed electrician’s help for proper installation.
For emergencies, a simple wood stove or a propane gas heater will work just as well, but with a lot less hassle and lower cost!
Title image by unlimidev