Heat pumps - cost £7,500 to £15,000
fuel: 15p/kWh; CO2: 0.6kg CO2e/kWh (if on Grid electricity)
Heat pumps extract heat from the air/ground/water to provide warmth in the same way that a fridge extracts heat from its inside to create coolth. They are able to create heat even when the temperature is as low as -15°C, although they are inefficient at low temperatures.
Heat pumps need electricity to run and so have some impact on the environment, but theoretically the heat they extract is constantly being renewed naturally. However, the long-term effects of ground source heat pumps on the average temperature of the ground, particularly if densely installed, is unknown.
Heat pumps come in 3 forms:
- and less often water source (WSHP).
The heat they extract can be used to heat radiators, underfloor heating systems, warm air convectors, and hot water in your home. Unlike gas and oil boilers, heat pumps deliver heat at low temperatures over long periods - during the winter they may need to be on constantly to heat your home efficiently. Since it is low-grade heat of about 40°C it is best suited to underfloor heating or similar, as opposed to most radiators, which run at 70°C+.
Heat pumps require electricity to run – for this reason many people question whether they can truly be regarded as ‘renewable’, unless of course you are producing your own electricity from a renewable source.
Modern, well-designed heat pumps only need one unit of electricity to provide three or more units of heat, making them much more efficient than other electrical heating systems – this is known as their Coefficient of Performance, or COP. Be careful though, often manufacturers will quote COP rates that have been achieved when the heat pump is running in temperatures similar to those required – for instance when it is 14°C outside and you want it to be 20°C inside.
At times during midwinter when it is sub-zero outside, the COP can drop dramatically and suddenly the heat pump gets very expensive to run – remember UK grid electricity is over twice as expensive as gas, and nearly four times as carbon intensive. For this reason be very careful about opting for an air-source heat pump – at least the ground stays at a steady 12°C. (Although be warned, GSHPs are still a relatively new technology and it is not known whether they will cool the ground over time, especially if pipes are densely installed in an area – after all, they rely on the sun warming up the ground again.)
If however you are replacing oil or electric powered heating and have limited alternative options for whatever reason, then Heat Pumps may well be the best solution for you – be sure to make your home as heat efficient in the first place though! [See our 'How to Use Less Energy' Section]
Advantages & considerations:
· Could lower your fuel bills and emissions, depending upon what fuel you are replacing.
· Could provide you with an income through the RHI.
· No fuel deliveries.
· Require little maintenance - ‘fit and forget’.
However, before opting for a heat pump, consider the following:
· It is essential that your home is well insulated and draught-proofed for the heating system to be effective, since heat pumps work best when producing heat at a lower temperature than traditional boilers.
· The system will pay for itself more quickly if it's replacing an electricity or coal heating system - heat pumps may not be the best option for homes on mains gas, and certainly not if biomass is a viable option.
· Heat pumps can perform better with underfloor heating systems or warm air heating than with radiator-based systems because of the lower water temperatures required.
· Combining the installation of a heat pump with other building work can reduce the cost of installing the system.
Costs and savings will differ dramatically depending on the size of pump, your home’s heat requirement, the distribution system, and the fuel that it is replacing – and in many cases a heat pump may prove to be more costly than the system it replaces.
This technology is an eligible measure under the Green Deal, and you should be able to receive payments for the heat you generate using a heat pump through the RHI.
Generally, heat pump installations are considered Permitted Development, although ASHP installations In Wales and Northern Ireland require planning permission, and in England and Scotland they must comply with certain criteria - check with your local planning office for details.
If you believe heat pumps are the best option for you, we advise that you check over all of the sums with an independent heating engineer before taking the plunge.
The Microgeneration Certification Scheme (MCS) has a list of certificated installers – you will need to use an MCS registered installer in order to qualify for the RHI.
NOTE: Units using hydrofluorocarbon (HFC) refrigerants are often marketed as low energy or a sustainable technology, however the HFC has a high global warming potential (GWP) and ozone depletion potential (ODP) if it leaks out. The R-22 refrigerant is being phased-out, to be replaced with more environmentally sound R-410A refrigerant – be sure to check!
Air source heat pumps
ASHPs absorb heat from the outside air, even when the temperature is as low as -15°C. However at these temperatures the COP will drop dramatically from that advertised, and the heat pump will become very costly to run – it is better to rely on an alternative heat source below 0°C.
ASHPs come in 2 basic types:
An air-to-water system can distribute heat via standard radiators. However, heat pumps work more efficiently when they generate lower temperatures than a standard boiler, so are more suitable for underfloor heating, which runs much cooler for longer.
An air-to-air system produces warm air which is circulated by fans to heat your home. An air-to-air system is unlikely to provide you with hot water as well, although having an air-to-water provide hot water is far from ideal because of the temperature required.
ASHPs are generally easier to install than a GSHP, although efficiencies will be lower. You'll need a place outside where the unit can be fitted to a wall or placed on the ground, with plenty of space around it for a good flow of air. Sunny walls are ideal.
Heat pump systems typically come with a warranty of two to three years, although with regular scheduled maintenance you can expect an ASHP to operate for 20 years or more.It’s worth checking the unit annually to clear leaves, debris, and any plants growing close by, and a professional installer should carry out a detailed check of the workings every five years.
Ground source heat pumps (GSHPs)
GSHPs use pipes which are buried in the ground to extract heat. If you decide to go for a GSHP you will have a further decision to make – whether to go for horizontal loops or a vertical borehole.
The size of your home and the amount of heat you need will inform the decision, as will the length of a horizontal ground loop required - if space is limited, a vertical borehole can be drilled instead.
The horizontal loop is laid coiled in trenches about two metres deep, and the vertical loop is dug down into the ground to a depth of up to 120 metres. As a rule of thumb, either system will require about 10m of loop per kW of heat required.
The earth must be of a certain quality for GSHPs. This is especially true of the vertical bore, which cannot be drilled into gravel or bedrock, or any ground that experiences regular high water transference – this washes away the heat!
Obviously the horizontal method requires large tracts of your garden to be dug up. Although this is cheaper than drilling a borehole, vertical GSHPs are more efficient. Both horizontal and vertical options will require access for machinery during installation.
Unlike the air, the ground below the surface stays at a fairly constant temperature all year round, so the heat pump can be used even in the middle of winter without the need for an auxiliary heating system.
Unlike an ASHP there is little the homeowner can do in the way of maintenance checks, although you are advised to consult with your supplier for exact maintenance requirements before you commit to installing a GSHP. Routine maintenance requirements may include pre-heating season checks of the water pump, external pipes and fittings and electronics.