Heat Pumps

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.

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 – around 40 to 50 degrees.  This works best with underfloor heating.  If you don’t or can’t have underfloor heating, your radiators will need replacing with thicker, larger radiators.  This is obviously a compromise, but heat pumps work more efficiently at these lower temps, so if you can live with these changes, this is the best approach.
  • There are now “high temperature” air source heat pumps available, producing water up to 65°C, avoiding any changes to your radiators.  Until now, these have been less efficient, and more costly to install.  But there’s a new generation coming out in 2020 that are claimed to achieve better efficiencies.  Awaiting costs and tech data.  This looks like an interesting development.  Info here.  Note that although some systems quote temperatures over 65°C, I don’t believe you qualify for the RHI grant unless the system is designed no higher than 65°C.  To see if this temperature will work with your system, try turning your oil boiler down to 65°C.
  • Heat pumps generally require the heating to be on for longer, because operating temperatures are lower than from conventional boilers.  If you have smart controls on your radiators which automatically heat up only the rooms you need to heat, a high temperature air heat pump may well be a better option, as high temp heat pumps operate at similar temperatures to traditional boilers.
  • 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 solar energy, not geothermal, even with boreholes.
  • 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.
  • Low maintenance, with no annual service needed.
  • Significantly costlier to install, 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.  Exact amounts depend on the system design, but find out roughly how much grant you get here.  The grants for ground source are around 50% higher than air source – to compensate for the higher outlay, and to reward you for the higher efficiencies.
  • The heat pump along with associated equipment sits inside the house, usually located where your oil or gas boiler current is.
  • There now appear to be some higher temperature ground source heat pumps entering the market, which could be suitable for older less well insulated properties.  e.g.  Stiebel Eltron .  Ask your installer.
  • 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.

More info:

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

If you really want to get into the detail, there’s an depth UK government report here..  Some key points:

  • Expect to pay around 10% to 20% installed cost for a high temp heat pump.
  • High temp can mean higher than 65°C, but then you don’t qualify for the RHI.
  • A number of trials suggest that heat pumps with flow temperatures of between 60 and 65°C can provide satisfactory heating using high temperature radiators systems with little modification.
  • Government studies suggest that the high temperature heat pump market is fairly mature, having been running in continental Europe for many years.  So don’t expect any significant cost savings by waiting for future models.
  • Heat pumps that achieve the high temp by “cascade” method with two pumps in series are more expensive.  Look for a monobloc design that achieves 65°C in one leap.
  • For air source heat pumps which reach 65°C, the installed costs are similar at £6,000 – £13,000, or £500 – £1200/kW
  • For Ground source products the total installed cost is estimated at between £10,000 and £40,000, or £1,000 – £2,000/kW – but with much bigger grants of up to nearly £30,000.

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

District Heating

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


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