WHAT SIZE AIR SOURCE HEAT PUMP? ARE THEY MORE EXPENSIVE TO INSTALL THAN A GAS BOILER?
This table illustrates how the size of your property and its insulation levels determine the size of air source heat pump you need: room-by-room heat loss calculation (MIS 3005 is the MCS installer standard for heat pumps and includes said heat loss calculation tool within it).
This calculation should be able to determine the maximum heat load at the design outdoor temperature as well as the amount of energy required to heat the home seasonally.
If the insulation is optimised and the emitters (radiators or underfloor heating) are also designed for low temperatures, then the flow temperature of the heat pump can be lower and therefore the efficiency will be higher. As such, the heat pump will cost you less to run.
Typically you can expect efficiencies of between 200% (at high flow temperatures of around 55°C) to around 400% (at low temperatures of around 35°C).
Hot water requires higher temperatures than space heating and as such the efficiency of a heat pump will be lower for hot water preparation than space heating.
Once you have the figure for space heating, an allowance must also be made for heating hot water. Allow around 50 litres of hot water per person per day.
To work out how much energy your home will use you can use a free spreadsheet calculator on MIS 3005 (for those with experience of spreadsheets). When you know the heat loss you will then be able to factor in the efficiency of the heat pump.
The installer has traditionally done the design work as well as the installation work but MCS has now changed to allow for specialist designers and specialist installers to undertake this (rather than one person trying to be a Jack of all trades).
The cost of a heat pump and the installation is more expensive than installing a gas boiler (this is the case for installation in both new and existing homes). Putting the costs into real context is not easy but the following costs (consisting of the system cost and installation) can be used for guidance:
● Combi boiler: £2,000 - £4,000
● System boiler with cylinder: £5,000 - £9,000.
WHAT IS THE PAYBACK PERIOD?
If you are introducing an air source heat pump into an existing home, the payback will largely depend on the actual cost of the swap, taking into account any savings you make through grants (see below) as well as accounting for how much you would have spent on a replacement boiler.
The running costs also need to be evaluated against the fuel that you are replacing. If you have a gas boiler running on natural mains gas, then there will currently not realistically be any financial saving but the carbon emissions saving is great. Against heating oil and LPG, the payback could be better but that depends on the cost of those fuels.