Heat pumps work like fridges in reverse. Powered by electricity, they concentrate heat from the air or the ground to heat your house and your hot water. And if you combine installation of a heat pump with switching to a green electricity tariff, you will be heating your home without carbon emissions.
The generous RHI grant has been extended due to Covid, so you have until March 2022 to complete your project. More here. With government debt soaring, it’s hard to imagine the successor to RHI being as generous.
Reduced 5% VAT
Not all contractors seem aware of this in my experience. A heat pump installation project should qualify for 5% VAT, including the cost of enabling building works, provided that material costs do not exceed 61% of the total project cost. If materials are greater than 60%, you still get 5% on the labour only. If you’re over 60 or on certain benefits, this 60% test doesn’t apply, and you qualify for 5% whatever.
If you’re using several contractors as well as your heating engineer (e.g. digger driver to dig trenches for the ground source piping, or a builder to alter a room to accommodate the heat pump), speak to your heating engineer about acting as main contractor. The other contractors will invoice at 20% VAT to your heating engineer who will then bill that work on to you at only 5%. This obviously involves admin and temporary cashflow costs for the heating engineer so expect a small charge to cover it – e.g. 2.5% commission.
5% VAT is also available if you’re doing work that is primarily designed to improve the insulation of your house.
VAT notice 708/6 – link
Air Source Heat Pumps
Air source heat pumps are units that sit outside your house extracting heat energy from the air. They can do this even when it’s below zero outside. Key points:
- Air source is less efficient than ground source, but much cheaper to install, and doesn’t need lots of land.
- The Renewable Heat Incentive (“RHI”) grant helps make heat pumps more affordable. It is paid in quarterly amounts for 7 years. Exact amounts depend on the system design, but find out roughly how much grant you get here.
- The system powered by electricity. This means that if you choose a green tariff, buying electricity from wind farms etc, your heating will be zero carbon.
- The running costs (in electricity) are said to be roughly the same as using gas, but this varies based on how well insulated your home is. Important to ask your installer for assurances on this.
- Low maintenance, with no annual service needed.
- They are now very quiet, so unlikely to be a noise issue for you or the neighbours. Your installer must carry out checks to ensure neighbours won’t be bothered.
- Most heat pumps produce relatively low temperature water. The lower the temperature, the more efficient. So they work best with underfloor heating at say 30ºC. If you don’t / can’t have underfloor heating, your radiators are likely to need replacing with thicker or larger radiators in order to heat the house with lower temperature water. There is a trade off available whereby, you can run the heat pump up to around 50ºC, which may allow you to keep some of the radiators, but then you lose some efficiency.
- In freezing conditions, the outside unit detects any build up of ice on the blades, and will momentarily run in reverse to clear it.
Ground Source Heat Pumps
Ground source heat pumps use an extensive network of pipes buried in your garden or a field to extract heat energy from the ground. The pipes are generally laid around 60cm deep. Alternatively you can install the pipes vertically in a series of boreholes (usually very expensive). Ground source works even when it’s below zero outside. Key points:
- More efficient than air source as the ground temperature is more stable through the winter.
- The heat you extract is from the solar warming of the ground, not geothermal, even with boreholes.
- The system is powered by electricity. This means that if you choose a green tariff, buying electricity from wind farms etc, your heating will be zero carbon.
- Low maintenance, with no regular annual service needed.
- Significantly costlier to install than air source, including groundworks requiring a digger to install the piping. But probably cheaper over the long term due to lower running costs and higher grants.
- If you’re already hiring machines to dig up the ground, it may not cost much more to lay the pipes. Really worth considering ground source for new houses or with significant extensions.
- Running costs are lower than air source, so lower than gas or oil. Which means savings to offset the higher outlay.
- The Renewable Heat Incentive (“RHI”) grant helps make heat pumps more affordable. It is paid in quarterly amounts for 7 years. The more efficient the SCOP rating of the heat pump, the higher the grant. Find out roughly how much grant you get here. The grants for ground source are around 50% higher than for air source – to compensate for the higher outlay, and to reward you for the higher efficiencies.
- Most heat pumps produce relatively low temperature water. The lower the temperature, the more efficient. So they work best with underfloor heating at say 30ºC. If you don’t / can’t have underfloor heating, your radiators are likely to need replacing with thicker or larger radiators so they can still heat the house with lower temperature water. There is a trade off available whereby, you can run the heat pump up to around 50º, which may allow you to keep some of the radiators, but then you lose some efficiency.
- The heat pump along with associated equipment sits inside the house, usually located where your oil or gas boiler currently is.
- Life spans are longer than air source – fewer moving parts.
- You’ll need to dig up a fair size area of ground for the pipes.
You will need an EPC to claim the RHI grant for putting in a heat pump. An Energy Performance Certificate (EPC) tells you how well insulated your home is, and what improvements could be made. Some installers recommend you have an EPC done before giving you a quote. If you’re not sure you have one, check this government website which holds all EPCs. Just enter your postcode, and you can download it. A previous owner may have had it done.
Costs & Running Costs
Good article here which reports on a trial of 89 systems by the Energy Saving Trust. Air source costs typically around the same as gas, and ground source from around 25% to 50% less than gas.
It claims air source installations range from £3,000 to £10,000, but I can tell you this goes up considerably for a bigger, older house. And ground source is quoted from £12,000 to £30,000. BUT then you get the RHI grant, which is considerably bigger for ground source heat pumps.
High Temperature Heat Pumps
Key points – though be cautious of any system advertised to run with flow temperatures hotter than 55ºC which may not qualify for the RHI grant. More info here.
- For space heating, most heat pumps work in the range 35 – around 50º. This normally means you need larger radiators. Some pumps are now advertised as capable of producing water up to 80% which would mean you don’t have to change your radiators. But 1) efficiencies really suffer, and 2) if you go higher than 65º you don’t get ANY grant. Many pumps aren’t even certified for the RHI at above 55º though this may be changing.
- But having researched this extensively, I couldn’t find a manufacturer or installer that will advise designing a system to run hotter than 55º. The worry is that the heat pump might wear out too quickly if it’s pushed at high temps all the temp. But technology is moving on so don’t rule it out.
- Heat pumps that achieve the high temp by “cascade” method with two pumps in series are more expensive. Look for a monobloc design that achieve the desired temp in one leap. But then it may be worth paying more to avoid the cost and disruption of having to upgrade radiators.
Three Phase Electricity
If your house is quite large, and maybe you also have electric cars, you might need a higher capacity electricity supply. Residential houses are nearly always on regular single phase electricity, but you can upgrade to three phase electricity, tripling the capacity. Unfortunately Western Power charge you quite a lot for this. Prices really vary depending on how far you are from the nearest supply. Think upwards of £5 – 10,000!
Important: When getting a quote for a heat pump, ask the installer if they’re sure you have enough electricity capacity on regular single phase. I’ve had quotes where they didn’t mention anything about needing to upgrade to 3 phase….
Air source and ground source heating can be suitable for district heating, where one large system supplies multiple houses and flats. The advantage of district heating is that there are savings on installation and maintenance by having one large system instead of multiple smaller systems.
I have found these installers in the local area – click here