Everything you need to know about the wild world of heat pumps

The concept behind heat pumps is simple: powered by electricity, they move heat around to either cool or heat buildings. It’s not a new idea—they were invented in the 1850s and have been used in homes since the 1960s. But all of a sudden, they’ve become the hottest home appliance, shoved into the spotlight by the potential for cost savings and climate benefits, as well as by recent policy incentives. 

Simple though the basic idea may be, the details of how heat pumps work are fascinating. In the name of controlling your home’s temperature, this device can almost seem to break the laws of physics. Heat pumps are also getting better: new models are more efficient and better able to handle cold weather. 

So let’s dive in and uncover what makes a heat pump tick.  

How does a heat pump work?

At a high level, a heat pump gathers heat from one place and puts it in another place. We’ll mostly talk about heat pumps in the context of heating, but they can also be used for cooling, gathering heat from inside and sending it outside like an air conditioner. Many heat pumps can actually be run in reverse, either heating or cooling depending on what’s needed. 

The hero in a heat pump is the refrigerant: a fluid that moves in a circuit, soaking up and releasing heat as it goes. Electricity powers the system, pushing the refrigerant around the cycle. 

As the refrigerant moves through the heat pump, it’s compressed and expanded, switching between liquid and gas forms to allow it to gather and release heat at different points in the cycle. (If this is enough detail for you, feel free to skip to the next question. Otherwise, join me on a journey inside a heat pump to understand how this all works.)

INTERNATIONAL ENERGY AGENCY

Picture this: it’s a chilly winter day, say 25 °F (-5 °C). You’re sitting on the couch in your living room with a good book, and your cat is curled up nearby. You look over at the thermostat, which is set to 68 °F. Sensible, but a little chilly. You walk over and bump it up a bit, to 70 °F. 

Your heat pump has been quietly humming along in the background. Now it kicks things up a notch to raise the temperature: the fan and compressor inside speed up, and the refrigerant starts moving faster to transfer more heat from outside to inside.