What Type of Heat Pump Would Work in My Home?
It’s a greener alternative to a traditional boiler, but what are the pros and cons? Here’s what you need to know
One of the key eco alternatives will be installing an electric heat pump to run our central heating systems. However, many of us still aren’t familiar with these green heating devices.
We asked three experts about the two main types: air and ground source heat pumps. How do they work, which properties do they work in, what might you spend or save on heating costs, and what are the overall pros and cons?
Professional advice from: Kit Knowles, director of Ecospheric, experts in Passivhaus and zero energy design; Mark Wilkins, technologies and training director of Vaillant, experts in installing heat pumps; and energy-efficiency expert David Hilton of Heat and Energy
Heat pumps might sound new and overwhelming, but David Hilton explains that we’re already using the same technology in our fridges.
“A heat pump works in the same way, but in reverse,” he says. “Just as your fridge moves heat from inside the box to outside the box, the heat pump is moving the heat from outside the box into it – it’s just that the box is your house. It isn’t creating heat, it’s simply moving it from one place to another, and turning it into a more usable form.”
This heat energy is extracted from the air, ground or water and used to warm radiators or provide hot water.
Do you feel strangely tied to your creaking old boiler, and worried about staying toasty in winter or having that daily hot shower? “If the question is, can you maintain your current lifestyle with a heat pump, the answer is absolutely yes, no problem – it’s all in the design,” Kit Knowles says.
“Air source heat pumps contain a fan that draws in the ambient air from outside the home, which heats a refrigerant within the heat pump,” Mark Wilkins says. “This is compressed to create a high temperature, which is transferred to the water in your heating system and sent to the radiators to heat your property.”
This type of pump is installed on the exterior wall or roof of your home, or can stand alone – the boxes can look a little like an air conditioning unit. “They vary in physical size depending on the power required: most can fit under a window outside a property and connect to a variety of components inside,” Mark says. “They can even be installed on balconies.”
If you’re worried about the noise, he says they’re usually “extremely quiet”.
According to Kit, the components that sit inside and outside air source pumps are changing and improving.
“You don’t have put them halfway up a wall looking industrial and ugly,” he says. “The new models coming out are sleeker and winning design awards. They can also be mounted in a louvred box. We have a sheet we give to clients on 10 different ways to screen heat pumps.”
This type of pump extracts heat energy from the ground. It typically requires a large amount of outside space for ‘ground arrays’ that are buried under the earth.
“A ground array consists of a series of pipes that are installed between 1.5m and 3m underground,” Mark says. “The pipes then absorb thermal energy from the ground.
“Although the installation does require digging trenches, the finished installation will not be noticeable, and any turf can be replaced or reseeded once completed,” he says.
Ground source heat pumps are installed inside a property and look similar to a freestanding fridge.
You might also enjoy 5 Excellent Sustainable Ideas From Our Tours.
“Heat pumps do require a larger capital investment than a traditional boiler,” Mark says.
It varies, but the average air source heat pump is thought to cost between £8,000 and £14,000, according to the Energy Saving Trust. By comparison, a typical new gas boiler with thermostatic radiator valves costs around £2,300.
Ground source heat pumps are even more expensive than air source. “They have a much larger capital investment, as the ground loop needs installing,” Mark explains.
That might all sound alarming, but prices are likely to drop considerably as heat pumps become a more mainstream option.
In time, homeowners can also expect to recoup costs through lower bills. That said, fluctuating prices make savings hard to predict, David says. He estimates that this winter, for example, those with heat pumps could be worse off than expected, due to higher-than-expected electricity costs.
The answer to this question is yes. “You’ll require space inside the property for a hot-water cylinder and, depending on the system, a small buffer tank, too,” Mark says.
“While pumps are effective at producing heat, you need a large device if you want to produce energy instantaneously,” Kit says. “A buffer vessel such as a tank allows you to have a smaller device.”
Up to 70% of gas-heated homes in the UK got rid of water tanks in recent decades and installed combi boilers. If you’re short on space, your bathroom is small, or you’ve converted your loft, this might be a hurdle.
That said, engineers are looking into ways to provide pumps without water tanks, so this issue might be solved soon. “You don’t have to have a water tank, but there are benefits,” Kit says.
Make the challenge of finding the right people for your project easier by searching the Houzz Professionals Directory.
“Air source heat pumps are the most common type, because they’re suitable for most properties,” Mark says.
“This is thanks to the minimal space they require in comparison with ground source pumps, making them suitable for even the smallest flats and terraced housing,” he says.
“Air source pumps are cheaper, quicker and easier to install,” Kit agrees. “And they’re not remotely difficult to retrofit or use in new builds. Also, if the design is inaccurate, the consequences are less dire than with a ground source.”
A ground source pump requires more space outside, and involves greater disruption for installation, so it might be a better option if you’re having a major overhaul or building your own property.
“They come in two forms – vertical or horizontal loops,” Kit says. “With a vertical loop, you use a piling machine to drill a deep hole. These are more resilient to sub-ambient freezing, but need more specialist equipment. The horizontal is more like a sink laid in a trench dug out to 1.5m to 2m. They are most sensible if you’re already doing ground works to a site.”
“Borehole systems are better suited to properties that have limited land space and aren’t suitable for a ground array,” Mark says. “Boreholes are created by drilling a hole up to 100m deep into the ground. The amount of ground loop required depends on the amount of heat energy you need to take from the ground, but once you get past 12m, the ground temperature is stable. The greater the heating demand of the property, the more ground loop will be required.”
“The most important benefit of a heat pump is that they have zero emissions at the point of use, so they can help homeowners to reduce their carbon footprint,” Mark says. “Many of us don’t realise that 31% of emissions from the home come from heating.”
Pumps can be extremely energy efficient, so should hopefully lower your future bills. “A heat pump’s efficiency is called a COP, or coefficient of performance,” David says. When it comes to choosing on pure efficiency, SCOPS (seasonal coefficients of performance) are better for ground source pumps than air pumps, if designed properly.
“Electricity is used to power the heat pump, and for every 1 kilowatt of electricity used by the heat pump, the property can get up to 5 kilowatts of heat in return,” Mark says.
“Essentially, they’re a very efficient use of electricity when you want to produce heat –around a third of the energy you would otherwise require.” Kit says. “They’re great as part of an overall solution.”
Other possible benefits include less maintenance than a boiler, and no danger of gases such as carbon monoxide in your home.
A ground pump has other pros. “It removes the need for fuel to be delivered and stored at home, which is common in homes that are in off-grid areas, where many households rely on alternative fuels, such as oil,” Mark says.
“A property may need to be upgraded before it’s suitable for a heat pump,” Mark says.
This is particularly true in the UK, where many of us live in draughty Victorian homes.
“The crucial thing is for a home to be well insulated and airtight, with no gaps,” David says. “In my opinion, 80% of the homes in this country are not really suitable. If you’re doing a lot of remodelling in your house, that’s a time to consider it.”
David also points out that heat pumps can struggle to achieve the same temperatures as traditional gas boilers. “If you’re changing from an existing boiler system that runs at high temperatures to a heat pump running at low temperatures, you’d probably have to change your radiator sizes,” he advises.
Accurate design that relates to the specifics of your home is also crucial. “Otherwise, you might not get the miles per gallon you’re looking for,” David says. “All these things are tested under controlled regimes, and replicating these scenarios in a house is difficult.”
For heat pumps to have a significant impact on the climate, Kit says additional action on the subsidising of the petrochemical industry needs to take place. “This is keeping electricity prices high and gas prices low, which is taking us in the wrong direction for this technology,” he says.
Kit also highlights the fact that heat pumps are not renewable in the same way as PV (solar) panels or wind turbines are. “You plug it in and power a pump and compressor like you do a fridge,” he explains, adding that we should be focusing more on conserving energy in our homes. “Passive design should be number one on the list for decarbonisation,” he says.
Do you have a heat pump and has it worked for you? Share your thoughts and photos in the Comments.