Do Heat Pump Water Heaters Need Ducting?
Do Heat Pump Water Heaters Need Ducting? In most cases, a heat pump water heater does not need ducting. Lots of units can just draw in air from the same room they’re in and then blow the cooler air back out into the same space. Of course, ducting can be useful, or even necessary, if the space where you’re installing the heater is too small, you want to take air from or blow air out to a different spot, or if the manufacturers have specific ducted arrangements they’re insisting on.
How does an unducted heat pump water heater work?
An integrated heat pump water heater is a unit that uses a fan to pull air across a thing called an evaporator – think of it like a bit of a heat collector. The refrigerant circuit then sucks the heat out of that air and transfers it over to the hot water in the tank. Once it’s done taking the heat out, the air coming out of the heat pump is cooler than what went in.
When you’ve got an unducted installation, both of these things happen right there in the same room. The unit pulls in air from around it, blows it through the evaporator and then sends the cooler air back out into the same space. And this can work just fine in a fairly big utility room, garage or plant room where there’s enough air circulating around.
If your property has relatively modest hot water requirements, consider the 100 litre wall mounted air source hot water heat pump.
For larger residential properties, our range includes a 200 litre air source domestic hot water heater and 300 litre air source domestic hot water heater.
For commercial premises and high-demand properties, explore the 400 litre air source commercial hot water heater or 500 litre air source commercial hot water heater.
When is ducting the way to go?
Ducting lets you have a bit more say in where the heat pump gets its air from and where the cooler air goes. For example, you might install the tank in a utility room but then duct the cold exhaust air to some other spot. Some units also let you duct the air coming in from somewhere else.
It really depends on the specific model of heat pump water heater you’ve got, but you might be able to duct:
Just the air coming in
Just the air going out
Both of them
Not every unit will support all three options, so you need to check the manufacturer’s installation instructions.
Can a heat pump water heater go in a small cupboard?
This is another good place to consider ducting. If you put an unducted heat pump water heater in a really small cupboard, it’ll quickly start sucking heat out of the little bit of air around it. Which means the room temperature will start dropping, and the heat pump will have to work harder to get the heat out of the even colder air. This will lower the overall efficiency of the unit, make it take longer to heat up, and reduce its Coefficient of Performance.
Manufacturers will often give specific guidelines about the minimum room size, ventilation requirements or ducting needed for their heat pumps. Just sticking some ventilation grilles in the cupboard isn’t enough; you really need to follow the manufacturer’s specific requirements.
Does ducting improve efficiency?
It can, but only if the ducting is set up to provide access to a better air source, and it’s properly designed. If the heat pump has some nice warm air to draw from, then it’ll generally run more efficiently than the same unit drawing from cold air. However, at the same time, ductwork can add resistance to airflow.
If the ducts are too long, too small or have too many bends in them, it can make the fan work harder and get less air past the evaporator – which will reduce the overall performance. For this reason, manufacturers usually specify exact duct diameter and limits for duct length, bends and overall resistance.
Can the air be ducted outside?
Some heat pump water heaters are designed to use outside air, but it really depends on the model. Using outside air means you avoid cooling the room, which can be useful during winter when you don’t want to lose heat from the building.
But the trade off is that outside air can be freezing cold – and as the temperature falls, the heat pump has to work even harder to produce the same hot water temperature. Cold and damp outside air can also cause frost to form on the evaporator, meaning some units will sometimes need to run a defrost cycle.
So before you decide to use outside air, you need to check the operating temperature range of the heat pump.
What about the cold exhaust air?
It’s funny how often the cold air produced by a heat pump water heater gets overlooked during installation. If you just dump it into a garage or utility room, the cooling effect won’t be too much of a problem and can even be useful – the heat pump removes moisture from the air as it operates, so it provides a bit of dehumidification. But in other locations, that cooling might be a problem.
Ducting the exhaust air away can stop a small room from getting too chilly and give you more options when it comes to where you install the cylinder. Just remember that the heat pump will produce condensate, so you’ll need to set up a suitable drain regardless of whether the unit is ducted or unducted.
Should I choose a ducted or unducted installation?
**An unducted installation is often the simplest option where the heat pump water heater is just going in a big garage, utility room or plant area with plenty of airflow. Ducting will give you a bit more control over where the air comes from and where it goes, but it’s more useful when space is limited or you really need to know exactly where the air is coming from and going to.** The really important thing is to build the air arrangement around the specific heat pump water heater in question. First, check the manufacturer’s guidelines for minimum room volume, airflow, duct size, max duct length and operating air temps.
Getting good airflow is crucial here – whether you’re ducting it in or leaving it unducted, just make sure you’re allowing that heat pump to draw in some air properly. This will keep its hot water recovery on track and its energy efficiency in check.