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Carolina Climate Control Blog

How Can a Heat Pump Work When It’s Cold Outside?


This is the #1 question HVAC folks like us get when discussing the benefits of using heat pumps for year-round comfort. We fully understand why people are a bit confused when they hear that there’s a type of comfort system that uses refrigeration technology to provide heat. When they hear more details about how a heat pump delivers heat, they may feel more confused.

We’re going to walk you through this with a hypothetical dialogue between a potential customer and a technician. We’ll pinpoint the confusion and show you why we think heat pumps in Charleston, SC are often the best choice for home comfort.

Customer: Okay, so what I understand so far is that a heat pump is similar to an air conditioner, except it can both cool and heat. But how does it heat if it works like an AC?

Technician: Think about how an air conditioner runs. You get cool air sent around inside. When you stand near the outdoor condenser, you’ll feel hot air getting blown out of it. The air conditioner removed that heat from inside the house—which is why the indoor air cooled down—and then pushed that heat outdoors. A heat pump can switch the direction it works so the opposite happens: heat is removed from the outside air and then sent into the indoor air. 

Customer: Ah, that does make sense. Sort of like swapping the job of the indoor and outdoor parts. But, wait a minute…

Technician: I think I know what you’re about to ask.

Customer: If the heat pump is removing heat from outside, where is the heat coming from? I would only want to run the heat pump in heating mode when the air outside is cold! 

Technician: The simple answer is that there is always some heat energy available in the air, no matter how cold it is. The only temperature where there’s no heat is absolute zero, and that’s an impossible temperature to reach. 

Customer: So if it’s 40°F outside my house, my heat pump can still bring in enough heat to keep the house warm?

Technician: Absolutely. The way the heat pump removes heat from the air is that it runs cold refrigerant through the outdoor coil. The refrigerant evaporates when it meets warmer air and absorbs heat. The temperature of the refrigerant in the outdoor coil when a heat pump is in heating mode is much colder than 40°F, so the heat pump won’t have a problem drawing on enough heat to keep your house warm.

Customer: What if the outdoor temperature goes lower than the refrigerant temperature?

Technician: There is something called the economic balance point where the outdoor temperature is too cold for the heat pump to efficiently remove heat. It can still heat the house, but it will work harder. However, that temperature is usually below freezing, depending on humidity.

Customer: It doesn’t get that cold often here in Charleston.

Technician: Which is why heat pumps are great for our climate. They work excellently in places with mild winters and can save money compared to using an electric furnace or sometimes even a gas furnace.

Customer: Wow, I’m glad I don’t live in a much colder place!

Technician: Aren’t we all?

Want to know more details? Then reach out to Carolina Climate Control. The Moose Is Loose in Your Neighborhood!

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