If you’re thinking about applying for the Green Homes Grant, you may have heard of an air source or ground source heat pump. But what is it and how can it heat your home?
Image: Vitocal 100-A air source heat pump, Viessman
As part of the Government’s new Green Homes Grant, vouchers of up to £5,000, or £10,000 for low-income households, are available for those looking to install a heat pump in their home as an alternative to, or to work alongside, a traditional gas boiler.
If you’re not sure what a heat pump is, chances are you’re not alone. Despite heat pumps having been around for a number of years, they’re still a technology that has not been adopted widely into the everyday home.
We’re breaking down all the information you need to know to figure out whether an air source or ground source heat pump is right for you.
Read more: The Green Homes Grant
What is a heat pump?
Image: Greenstore Low Energy circulation pump for ground source heat pump, Worcester Bosch
In basic terms, a heat pump system is a method for heating your home using equipment which harnesses the natural temperature of either the air or the earth. With that in mind, there are broadly two types of ground source heat pump – an air source heat pump or a ground source heat pump.
An air source heat pump is located above the ground, and would be attached to the side of your home. This heat pump absorbs heat from the outside air, even where it’s at lower temperatures. This is then compressed by the system to raise its temperature, which can be then used to heat your home. An air to water heat pump will transfer this heat to water, which can be used for low-flow radiators, underfloor heating and your hot water, while an air to air heat pump will directly warm the air of your home.
A ground source heat pump collects heat through a series of plastic pipes, laid in the ground within the top few metres of the surface. At this depth, the temperature of the ground is pretty constant between 7°C and 10°C, no matter the temperature above-ground. Again, the heat collected is then compressed to increase the temperature, before this heat is extracted and transferred to the pump, ready to be sent to radiators, underfloor heating and hot water storage.
What are the benefits?
Heat pumps are a renewable energy source for the home, and one that can lead to huge savings on your home’s carbon footprint, in some cases up to 50% from a traditional gas boiler. These systems are fairly reliable - they operate like a fridge, but in reverse, and the technology will rarely go wrong with annual checks and maintenance.
There are some energy saving costs to be had for some, but not all heat pumps.
Due to their renewable nature, heat pumps are eligible for a range of Government schemes to help compensate for the initial cost outlay, including the Green Homes Grant and the Renewable Heat Incentive, which can help to cover costs of making the transition to a greener energy for your home.
What are the drawbacks?
Image: Ultra Quiet Ecodan air source heat pump, Mitsubishi
While an air source heat pump is relatively easy to install with minimal upheaval, a ground source heat pump installation can be a costly and disruptive. An air source heat pump has quite a small footprint on the exterior and interior of your home, however a ground source heat pump unit is much larger, requiring more space. All this may lead to the conclusion that air source heat pumps are a better option for retrofitting a property.
There have historically been some complaints about the noise of air source heat pumps which dictates where they can be placed under permitted development rules, however, modern technology has improved on this, with many air source heat pumps now designed with quieter technology.
Compared to a traditional gas boiler, the temperatures a heat pump produces is more efficient at a lower temperature. This means that it works better with underfloor heating and radiators suited to its flow temperature, so some radiators may need to be changed to suit the new heating type. This may also lower the top temperature your home’s hot water system is able to produce.
Would a heat pump work for my home?
Image: Daniela Exley for Good Homes
Because of the lower temperature produced by a heat pump, they work best with homes that are well insulated and air-tight, making less of a demand on a home’s heating system. With this in mind, to get the best results from a heat pump, your home should be well insulated and have energy efficient windows and doors, so that our home has a healthy EPC report. Your home’s last EPC report can be checked via the Simple Energy Advice website as part of your Green Home’s Grant application.
Read more: How to apply for the Green Homes Grant
For installing a ground source heat pump where pipes are laid in narrow trenches, you’ll require a large amount of land. A typical 8kW output heat pump would require 200 metres of trench, across several loops, meaning an overall area of 400 square metres required. There are also options to lay pipes vertically, much deeper into the ground, however this requires specialist equipment to drill boreholes which can be an expensive process.
How much do they cost?
The cost of the heat pump, installation and potential groundworks vary depending on the type of pump and the home it’s being installed in.
According to green energy comparison site Green Match, the cost for a heat pump and insulation for a 4-bedroom home is approximately £21,000, with a further £3,000 attributed to groundworks. Green Match also suggests that this will result in energy savings of between £440 - £660 per year compared to a gas-powered home.
A ground source heat pump is eligible for the Green Homes Grant as a primary measure, meaning that the full £5,000 or £10,000 could be claimed against the cost. A ground source heat pump is also eligible for the RHI, which sees quarterly payments over seven years. These depend on the technology and site, but have one of the highest tariffs for any technology.
The average price for installation of an air source heat pump is between £8,000 and £18,000 for an air-to-air source heat pump and £7,000 and £11,000 for an air-to-water source heat pump. A four bedroom house with an air source heat pump will see annual heating costs starting from £759 per year, which is not a significant difference to a gas boiler, but with RHI payback of up to £1,600 per year.
It’s worth noting that if you apply for both the Green Homes Grant and the Renewable Heat Incentive, the value of your Green Homes Grant application will be taken from your RHI repayments.