Are Ground Source Heat Pumps or Air Source Heat Pumps the future of UK home heating systems? What is the actual installation cost?
With the plans for the UK to cut its carbon emissions by 78% by 2035 and to net zero by 2050, there is an urgent need to rethink how homes in the UK are heated. According to the Office of National Statistics (https://www.ons.gov.uk/peoplepopulationandcommunity/housing/articles/energyefficiencyofhousinginenglandandwales/2020-09-23), approximately eight in ten homes in England are heated by gas boilers supplied from the gas grid. Unfortunately, even efficient gas boilers inevitably emit carbon dioxide, so a shift to net zero will require gas boilers to be phased out as soon as possible. Existing homes also need their insulation to be upgraded so they can be heated more efficiently.
Hydrogen boilers have been proposed as a replacement for gas boilers, however, domestic hydrogen boilers are not available yet in the UK and the country doesn’t have a hydrogen gas grid. An alternative which is readily available in the UK and widely used in other parts of the world are heat pumps. According to the UK government’s Climate Change Committee report Policies for the Sixth Carbon Budget and Net Zero (https://www.theccc.org.uk/wp-content/uploads/2020/12/Policies-for-the-Sixth-Carbon-Budget-and-Net-Zero.pdf) the UK needs to be installing more than a million heat pumps each year by 2030 to make the necessary shift in its carbon emissions. Currently less than one in 100 homes in England is heated by a heat pump.
Heat pumps concentrate heat from outside and transfer it into a home – a bit like a fridge working in reverse. They are most efficient when operating at a lower temperature than a gas boiler, so work best with a very well insulated home. Heat pumps for heating your home and providing hot water come in three basic types – air source heat pumps, ground source heat pumps and water source heat pumps. Air source heat pumps extract heat from air, working even when temperatures outside are freezing. Ground source heat pumps extract heat from the ground. Water source heat pumps extract heat from a water body. Water source heat pumps require direct access to a river or lake so are unsuitable for most households. Air and ground source heat pumps, however, are suitable for homes with some outside space.
An air source heat pump needs an outdoor unit a couple of square metres in size with a good flow of air around it. A ground source heat pump requires loop of pipe to be buried in the ground in which a saline liquid can be circulated to gather heat. The loop is either buried vertically in a bore hole or horizontally in a trench. Ground source heat pumps are generally more efficient and cheaper to run than an air source heat pump because the ground temperature varies little over the course of a year, unlike the outside air temperature which is coldest when you most need heat for your home.
According to the Energy Saving Trust (https://energysavingtrust.org.uk/energy-at-home/generating-renewable-energy/), a ground source heat pump typically costs between £14,000 and £19,000 to install, with horizontal ground loops cheaper to install than vertical loops in a bore hole. The Ground Source Heat Pump Association gives a similar installation cost estimate (https://www.gshp.org.uk/ground_source_heat_pumps_Domestic.html). There are some subsidies available from the government via the Renewable Heat Incentive scheme to reduce the final cost of both systems to the homeowner.
Currently I am renovating and extending a small 1930s bungalow house in a village near Guildford. As part of the building works we are insulating the house to Passive House renovation standards so that the house will need little heating and also be suitable for an efficient heat pump operating at a low temperature. As the house has a large flat garden with easy access and there is the space for a horizontal ground loop, we wanted to install a ground source heat pump as part of the renovation. I contacted a dozen heat pump suppliers to get quotes. So how did the quotes I received compare to the cost estimates of the ground source heat pumps provided by the Energy Saving Trust and the Ground Source Heat Pump Association?
Quote 1: £33,600 for the installation of a 9kW ground source heat pump, with estimated renewable heat incentive payment of £2,300 per year for seven years, and a £200 per year reduction in our heating bill.
Quote 2: £21,000 for the installation of a 9kW ground source heat pump. No renewable heat incentive payments since installer in not registered with scheme.
Quote 3: £21,700 for the installation of a 7kW ground source heat pump, with estimated renewable heat incentive payment of £2,100 per year for seven years, and a £400 per year reduction in our heating bill.
Quote 4: £21,100 for the installation of a 9kW ground source heat pump, with estimated renewable heat incentive payment of £2,600 per year for seven years, and a £300 per year reduction in our heating bill.
Quote 5: £24,900 for the installation of a 5.7kW ground source heat pump, with estimated renewable heat incentive payment of £1,500 per year for seven years and a £100 per year reduction in our heating bill.
Quote 6: £35,900 for the installation of a 6kW ground source heat pump.
Quote 7: £21,600 for the installation of a 6kW ground source heat pump, with estimated renewable heat incentive payment of £1,900 per year for seven years.
The heat pump installation quotes were all more than £21,000, so well above the upper end of the range suggested by the Energy Saving Trust and the Ground Source Heat Pump Association even though it is a small home. Even with the generous Renewable Heat Incentive subsidy payments we would receive from the government, none of the quotes made any financial sense compared to sticking with a gas boiler connected to the gas grid. Perhaps ground source heat pumps make sense for large houses with very high heat demands due to economies of scale but for a small house with low heat demands they clearly do not make sense, even with the government subsidy.
As a result of the excessive cost of getting a ground source heat pump, we decided to look at air source heat pumps. The Energy Saving Trust suggests that an air source heat pump typically costs £9,000 to £11,000. For these I got three quotes:
Quote A: £9,600 for a 9 kW air source heat pump.
Quote B: £9,381 for a 6 kW air source heat pump with estimated renewable heat incentive payment of £1,049 per year for seven years, and a £320 per year reduction in our heating bill.
Quote C: £7,818 for a 5 kW air source heat pump, with estimated renewable heat incentive payment of £1,020 per year for seven years.
We decided to go with Quote C since it made financial and environmental sense. The payments from the Renewable Heat Incentive over seven years should nearly cover the full cost of installing the heat pump, while the running costs would be slightly less than those of a new efficient gas boiler. Opting for an air source heat pump, if you can renovate your house so that it is well insulated, really does make sense.
