This transcript has been edited and condensed for clarity.

The following sentence doesn’t make any sense, but is actually true: A heat pump can turn 1 kilowatt-hour, or kWh, of electricity into up to 4 kWh of heat.

For the home heating and cooling technology known as the heat pump, this means big potential savings both for carbon emissions and for utility bills. Recently, I’ve been looking at two different questions: First, how good are heat pumps for the climate? And second, how much money do they save? 

The term heat pump is actually a little bit confusing. A heat pump is actually a super efficient heating and cooling machine. And the thing about a heat pump is that it doesn’t actually make heat — it moves it. 

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That sounds a bit weird, but this is how it works: If your house is too hot, a heat pump can basically take the heat from inside your house and put it outside. That’s exactly the same as an air conditioner. But if your house is too cold, a heat pump can also bring heat from outside into your house. And it can do that even if the outside air is really cold. 

The science here is a little bit complicated, but because a heat pump is moving heat, instead of creating it, it can reach efficiencies of 300 or 400 percent. A normal heating system, on the other hand, can only reach an efficiency of about 100 percent at best. Because of this efficiency superpower, heat pumps can actually save a whole bunch of greenhouse gases from spewing into the atmosphere. 

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According to the energy research group Carbon Switch, switching to a heat pump can save you anywhere from about 1 metric ton to about 7 metric tons of carbon emissions every single year. The carbon savings are the most dramatic if you have an old electric baseboard heater: In that case, you can save over 7 metric tons of carbon dioxide every year by switching to a heat pump.

For reference, if you went vegan for an entire year, you’d be saving about 1 metric ton of CO2-equivalent. If you skipped an international flight to Europe, you’d be saving a ton of CO2. But in this case, you don’t actually have to give up meat or your international travel plans to save carbon. You’re just ensuring a pleasant year-round environment.  

But let’s be real: Being a homeowner is expensive, and retrofitting your home heating system is often super expensive. So even with all these carbon- and climate-saving benefits, does switching to a heat pump make sense financially? 

First off, everyone’s house is different, and heat pumps, like houses, can come in all different shapes and sizes. They can be ductless or ducted. They can be geothermal, or air-source, or water-source. Some of them can even look like George Clooney.

Whether a heat pump makes sense for you is going to depend on what type of house you have, your existing fuel system, and all of these other little complicated details. But it turns out that for a lot of Americans, buying and installing a heat pump is going to make a lot of financial sense. To understand why, let’s crunch some numbers. 

Let’s say you’re a homeowner and your fuel oil furnace is near the end of its life. You’re trying to decide, “OK, do I buy a new, fuel-oil furnace or should I go for an air-source heat pump?”

According to the home repair site Fixr, for a 2000-square foot house, the average cost of buying and installing a new oil furnace is about $6,000. Buying and installing a new air-source heat pump that will fit into existing ducts, on the other hand, is about $10,500 — so nothing to sneeze at. But electricity is a lot cheaper than fuel oil. And don’t forget about the heat pump’s monster efficiency. 

Carbon Switch calculates that for the average homeowner, switching from a fuel oil furnace to an air-source heat pump will save about $950 every year in utility bills. That means that in less than five years, your heat pump will have actually paid for itself, and you’ll be saving almost $1,000 every year after that. And on top of that, you’ll also be saving about 4 tons of carbon dioxide from spewing into the atmosphere every single year. 

But for some people, buying and installing a heat pump isn’t going to make quite as much financial sense. Let’s say that you’re the same homeowner, but instead of fuel oil, your home is heated by a natural gas furnace. Actually, the prices for a gas furnace are about the same: $10,500 and $6,000. But natural gas in the U.S. is still pretty cheap — partly because we haven’t accounted for all the harms that it’s doing to our environment. 

Natural gas is only about one-third the cost of electricity. But remember how I said earlier that heat pumps are three to four times more efficient than any other heating system? That means that you’ll still be saving some money, just not quite as much. 

Again, based on those same earlier numbers from Carbon Switch, the average U.S. homeowner can expect to save around $104 a year if switching from a natural gas furnace to a heat pump. That makes switching to a heat pump a little bit less affordable, but it would still save carbon emissions — about 1.1 metric tons every year. And your heat pump will also double as an AC, so that could actually save you another $7,000 or so. 

Some utilities and cities are willing to give you rebates for up to a couple thousand dollars off the initial cost of buying and installing a heat pump. And if your home is heated by pretty much anything that’s not natural gas, you can expect to save between $800 to $1,200 a year on utility bills. 

And it’s important to remember that these averages are just averages. While the CO2 savings for heat pumps are pretty clear, the financial savings are a little bit more complex.

Each house, installer, and climate zone means something a little bit different for heat pumps. 

And if you’re anything like my editor, you’re probably asking yourself, “Is this system going to be able to keep up with these cold New England winters?”

Back in the 1980s, heat pumps were mostly installed in warm Southern states, where there was a need for air conditioning in the summer and just a little bit of heat in the winter. The common refrain was heat pumps don’t work below 40 degrees Fahrenheit. 

Now, a new technology known as variable speed compressors — which is basically just a way to speed up the flow of heat — means that there are now air-source heat pumps that work when the outside temperature is down to negative 31 degrees F. 

In Maine, a group called Efficiency Maine has given out rebates to help homeowners install about 100,000 heat pumps in one of our coldest states. That state now sells more heat pumps per capita than even the heat pump-crazy Scandinavian countries. 

Now, it is still true that some older or lower performance models still don’t work super well in the cold. So if your heat pump from 10 years ago doesn’t work in subzero temperatures, don’t be surprised. But if you get the right heat pump for your environment, and potentially have a backup source of heat for the really cold days, then heat pumps can pretty much carry you through. 

The bottom line is: The humble heat pump can save loads of CO2 emissions, it can keep you warm in the winter, it can keep you cool in the summer, and in lots of cases it can also save you money.