Do Heat Pump Water Heaters Cool Down the Room?

Do Heat Pump Water Heaters Cool Down the Room? Yes, a heat pump water heater can cool down the room it’s installed in if it pulls its air from the room and then blows the cooler air right back in there. That happens because a heat pump extracts heat from the surrounding air and puts it into your domestic hot water. So the air that comes out of the bit that cools things down is actually cooler than the air that went in. And how much the room cools down will depend on the size of the room, how much air is moving in and out, how good the heat pump is, how long it’s running, what the temperature of the air around it is, and whether you’ve got the air ducted or not.

Why do heat pump water heaters blow out cold air?

A heat pump water heater doesn’t make most of its heat from electricity. Instead, it’s taking heat that’s already in the surrounding air and using it to heat the water in the hot water cylinder.

To achieve that, a fan draws in some air and blows it across a cold bit called the evaporator, where the liquid inside the machine sucks up some heat from the air. That liquid is then pumped to a part that compresses it, which makes it hotter. Then it transfers that heat to the domestic hot water through another bit of the machine.

Because the machine has taken some heat out of the air that’s coming in, the air that’s coming out is cooler.

This is all just the normal way a heat pump works, and it doesn’t mean the machine is faulty.

You can find further technical and product information across our dedicated heat pump water heater pages:

Wall mounted domestic hot water heat pumps
Domestic hot water heat pumps
Commercial domestic hot water heat pumps

How much will a heat pump water heater cool my room?

There’s no single number that covers every situation, because how much the room temperature will drop depends on all sorts of factors.

Important things to think about include:

How big the room is?

How cold the air is to start with?

How much air is moving in and out?

What the heat pump is capable of?

How much air is actually getting past the thing that cools the air down?

How long the machine runs for?

How much heat is coming into the room from the rest of the house?

Whether you’re ducting the air in or out, or whether you’re just blowing it all back into the room

If you put a heat pump in a big garage or utility room, the temperature might not go down that much. But stick the same machine in a small cupboard and the temperature can drop a lot faster.

Does a colder room make a heat pump less efficient?

It’s possible, yes.

As the heat pump takes heat out of the room, the air gets colder, and that makes it harder for the machine to do its job. That means it’s going to be using more energy to get the hot water, and that might make it take longer to heat up.

That’s one of the reasons why the manufacturers tell you to make sure you’ve got enough room volume, and that there’s enough air moving around, and that the temperature in the room is okay.

If you don’t leave enough space for the machine to breathe, you can end up with a machine that’s not working properly – or at least, not as efficiently as it should be.

Can you duct the cold air outside?

Some heat pump water heaters come with air ducting, which lets you control where the machine gets its air from and where the cooler air goes. Depending on the machine, you might be able to get air from outside and blow the cold air outside, or you might be able to duct both the air in and the air out.

But you have to follow the manufacturer’s instructions for how to do that – and what kind of ducting you can use and where you can put it. If you make a mess of it, you might end up with a machine that’s not working properly.

Is the cooling effect from a heat pump water heater ever useful?

Yes, it can be.

In some situations, the heat pump can actually be useful for cooling and dehumidifying. When warm air passes over the cold thing that cools it down, some of the moisture in the air condenses out – and that creates condensate water that needs to be got rid of.

In some cases, having the heat pump in a utility area can actually be a bit of a bonus – it’ll cool and dehumidify the air as it heats the water. But don’t get the idea that a heat pump water heater is a substitute for a proper air-con system.

What happens in winter?

If you’re cooling an internally heated room in the UK, that’s probably not what you want in the winter. If the heat pump takes heat from the air inside the house, that means some of that heat might have been what was keeping the house warm in the first place. So you need to think about how all that works when you’re deciding whether a heat pump water heater is the right choice for you.

Using ducting or putting the machine in a space that’s a bit better ventilated can help manage that problem.

Is room cooling something to worry about with heat pump water heaters?

Usually not, as long as you choose the right machine and put it in the right place. The only time you might get a problem is if you’ve got a heat pump in a small or poorly ventilated space that’s not been set up properly. Before installation, take a good hard look at the manufacturer’s guidelines for minimum room size, airflow requirements and operating temperature – and don’t forget to sort out your ducting too. With a proper job getting the thing set up, your heat pump should be able to suck in the air it needs without letting the room temperature plummet – all the while churning out plenty of hot water for the house at a decent efficiency.