So, you’ve got a heating and cooling system in your home. There’s a metal box outside that makes noise, and you control it with the thermostat on the wall. Can you tell me right now whether it’s a heat pump or just an air conditioner? This is a really important question to be able to answer when you’re talking to an engineer or contractor at a cocktail party.
The diference between the two is simple. An air conditioner moves heat from inside your home to outside in the summer. A heat pump does that and also moves heat from outside to inside in winter. Really, what we call an air conditioner is just as much a heat pump as the device that owns the heat pump name. It’s just that the air conditioner pumps heat in only one direction. (Refrigerators and dehumidifiers do the same thing pretty much.)
Now, back to my question, do you or don’t you know what you have? If you don’t, here’s your opportunity to do a little snooping and find out. Here are three ways:
- Go outside and find the model number of the metal noisemaker (aka the condensing unit). Type that number into the search box in your browser and see what the all-wise Internets tell you about it. You might need to type in the brand name, too. That search should get you the answer.
- Go outside and peer down through the grill on top of the condensing unit. If you see a horizontal brass pipe similar to the one shown in the photo at right, you’ve got a heat pump. That piece is called the reversing valve, and it’s what allows a heat pump to pump heat in both directions. Note: If you look down in there and don’t see one, that doesn’t mean it’s not a heat pump. Sometimes they’re hidden behind the access panel outside the coil, as was the case for the one in the photo.
- Go inside and set your thermostat to heat. Adjust the temperature setting until the heat comes on in your home. Now go outside and see if the condensing unit is making noise and blowing air. If it is, you have a heat pump. (Note: This doesn’t always work, but something else about the thermostat tells you the answer, too. See first comment below.)
Now that you know what you have, you’ll never be embarrassed at cocktail parties again! When that contractor starts telling you about TXVs, subcooling, and superheat, or the engineer starts talking about mean radiant temperature, comfort, naked people, and building science (you have to watch out for those engineers!), you’ll be ready.
I suggest carrying a photo of your reversing valve with you at all times. I certainly do. I keep it right next to my card with 101 digits of pi and the photo of my pride and joy.