Will a Generator Run Your Heat Pump?

When facing a power outage, many people turn to generators to keep necessities such as refrigerators running. However, depending on the time of year your power outage occurs, you may be wondering can your generator power your heat pump. 

There are two main types of generators – portable and home standby generators. Portable generators are not designed to run major systems like heat pumps. Heat pump systems vary in size, and as the size increases, so do the amps required to run the heat pump system. Home standby generators are best suited for running a heat pump system. However, a few portable generators can power certain moderate-sized heat pump systems depending on the wattages of your system and the portable generator.

Let’s discuss how home standby and portable generators heat pumps, especially based on watts.

How Many Watts Does a Heat Pump Use?

Heat pumps provide heat by extracting warmth from outside the house and transmitting it inside. That means when it’s hot outside, the heat pump reverses its direction and functions like an air conditioner that takes away the heat inside your home. It is quite the process.

That’s why heat pumps and other electric furnaces usually require 15,000 watts (15 kW) or more to work. That’s huge compared to ordinary gas or oil-based air systems that can work with as little as 2500 watts (2.5 kW). You can calculate the specific watts your heat pump use with this formula:

volts x amps= watts

You can find the volts and amps used by your heat pump on the data tag or by looking at the breaker size inside the electrical panel box. Still, the answer to this formula would only be an estimate. Your heat pump doesn’t use the exact amount of volts and amps indicated on it. Just get a service tech to do the math for you for a much more accurate answer. 

According to an online document from Howell-Oregon Electric Coop, a 3-ton air source heat pump requires 7200 startup watts and 5400 running watts. This is in addition to other devices your generator may be running. You’ll need to total up the total startup watts to determine the total wattage for the generator you need.

What Generator Wattage Do You Need to Run a Heat Pump?

Since heat pumps typically use 15,000 watts (15 kW), no portable generator can certainly support that. This is a major household system that consumes a lot of normal electrical energy already. There is no way a small backup generator can supply power to make such a big system work. 

You need a stationary generator that’s at least 17,000 watts (17kW) to run a heat pump, whether it’s a standard one or a package unit. Your generator must have a higher wattage than your system because many appliances, including heating and cooling systems, need a power surge to start working.

This is also known as the starting wattage. The watts of your generator may be enough to run a heat pump, but its starting wattage is a separate thing that needs to rate higher than your system’s starting wattage or maximum output wattage.

If you don’t get a generator with a higher starting wage, you can electrically damage your system. These calculations give portable generators a little window for operating air systems then. Some larger models have enough running wattage to run mid-sized heating and air conditioning systems. 

However, small portable generators are a simple no-go as they can only power a few little things, not systems. If you’re seriously considering getting a portable generator for cost issues, make sure to calculate these starting and running wattages before buying one. Better yet, consult a licensed electrician to help you with your buying decisions. They are most likely to advise you to stick with stationary generators for safety. 

It’s also worth noting that since you’ll be needing a powerful generator to run your heat pump, you’ll also be consuming more fuel regularly. That means higher energy costs long-term. A 7000 watts (7 kW) generator will burn more fuel than a 22,000 watts (22 kW) generator during operation. When purchasing your generator, keep this in mind, as the initial purchase cost isn’t all there is. 

Can a Generator Run a Mini Split Ductless Heat Pump?

Mini-split ductless heat pumps are high-power systems despite being slightly less requiring watts to operate. This wall-mounted heat pump may be ductless, but it surely does consume quite the power as well. Many alternative home builders use mini-split ductless heat pumps for setups like trailer homes, and they use generators to power them. 

Mini-split ductless heat pumps can work with a portable generator’s power supply, but they’re only good for emergency purposes. Some people want to use generators as primary or secondary power suppliers for these heat pumps when they should be merely backups.

A Mitsubishi 1.5 ton mini-split ductless heat pump will need up to 5060 startup watts and 3960 running watts on a 20 amp. More if your mini-split system has multi-zone wall units.

Why Home Inspections Are Important

Should you need to run your mini-split ductless heat pump with your backup generator, here are the steps you should take:

  1. Look for the transfer switch that’s usually directly attached to the circuit of the furnace. If you don’t have a transfer switch installed between your circuit breaker and furnace, you can’t connect the generator at all. Contact an electrician to have one installed if you haven’t yet.
  2. You need to rewire the system by cutting the wire running from the furnace to the circuit breaker. Install an outlet to the breaker panel so the wires can run from the circuit breaker to the furnace. Spare an outlet to plug in the generator. 
  3. Installing the generator plug on the side of the furnace is the way to go. Plug the furnace in and reset the breaker to check if your furnace is still working the way it should. Double-check if the generator works with the furnace as well. 
  4. Don’t just put your generator anywhere close or convenient. It has to be in a safe location because it emits carbon monoxide which shouldn’t be trapped inside your home or in a closed garage. Avoid placing it where children and water can reach it. Just have an outdoor extension cord connect it to the furnace and never overload it in times of power outage or else the heat pump won’t work. 

How Does a Transfer Switch Work in Powering Heat Pumps with a Generator? Is It Important?

You’re probably wondering how transfer switches work in transmitting power from the generator to the heat pumps. You ought to know about it now before you commit mistakes to skip the expense of buying such a switch. Your heat pumps are directly connected to your power panel, so they definitely won’t work with extension cords no matter what hack you pull. 

Your transfer switch connects mainly to the circuit box or power panel. How it works is that it will feed that electricity from the generator directly into the house. You have to pick which circuits you want to turn on at this point, but you have to be careful not to overload your backup power supplier. 

Right now, you should know that transfer switches could even be as expensive as the generator itself. You can’t even DIY the installation as you need a professional to install it for you safely. This is not one of those things you can guess your way through. Otherwise, all your expenses on the generator and the switch would go down the drain. You could even damage your heating system and other related electrical units.

Installing a generator and transfer switch will require some electrical upgrades in older homes with older meter boxes.

A little tip hack some people do to avoid spending too much on the installation costs is by back-feeding the generating into your home. Back feeding a generator is hooking the generator right into an outlet in your home using a two-male-sided extension cord. However, this can be extremely risky not just for you but also for your neighbors and electrical workers. 

The power from the grid is likely to come back on, leaving you with two power sources running through your home without any circuit breaker to regulate it all. That could lead to a catastrophic overload resulting in a fire. This is exactly what the transfer switch saves you from. It can stop the power from the outside grid from reaching into your home. 

That way, you can be assured that there won’t be an overflow that could lead to a disastrous fire. This is the only safe way to back up your heat pump during a power outage. 


To sum it up, opt for a standby generator to power your heat pump at home. Never rely on portable generators unless you have a really small heating unit. If you’re still unsure of the best option for your heating system, please consult a trained electrician to get accurate advice on how to back up your home’s heating in times of emergency power outages. 

Make sure also to leave the installation processes to the professionals. Hire a licensed electrician for these tasks. Speaking of expenses, do not ever leave out the transfer switch in the budget. Back feeding is only going to cost you your entire home.

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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