Ask ten people whether a heat pump is cheaper to run than a gas boiler and you will get ten different answers, most of them confident and half of them wrong. The truth is that it depends on your electricity tariff, how well the system is designed and how leaky your house is. Here is how the sums actually work for a typical home in Cheshire.
A modern condensing gas boiler turns roughly 85 to 92 per cent of the gas it burns into useful heat. An air source heat pump does not burn anything; it moves heat from the outside air into your home, and for every unit of electricity it uses it typically delivers 2.5 to 4 units of heat over a year. That yearly figure is called the seasonal coefficient of performance, or SCOP.
The catch is price. Under recent Ofgem price caps, gas has sat somewhere around 6 to 7p per kWh while standard electricity has been closer to 24 to 27p per kWh. Electricity costs roughly three and a half to four times as much as gas per unit, so a heat pump needs an SCOP above about 3.5 just to break even on a standard tariff. A well designed system in a reasonably insulated house will get there. A poorly designed one will not.
A three bedroom semi in Northwich, Crewe or Macclesfield built between the 1930s and 1980s will often use 10,000 to 14,000 kWh of gas a year for heating and hot water. Call it 12,000 kWh. On gas that is roughly £850 to £1,000 a year at recent prices, including the boiler's standing charge.
Replace the boiler with a heat pump running at SCOP 3.2 and you need about 3,400 kWh of electricity for the same heat. On a standard tariff that is £850 to £950, so broadly level with gas. Switch to a dedicated heat pump tariff, of which several suppliers now offer, and the same heat can cost £550 to £700. Add in the fact that you no longer pay a gas standing charge, which is around £100 a year on its own, and the heat pump pulls ahead.
Bear in mind these are annual figures. A heat pump's bills are heavier in January and lighter in summer, and the winter months are where a badly sized unit shows itself. Cheshire winters are mild by UK standards, rarely dropping far below freezing for long, which suits heat pumps well.
The single biggest influence on heat pump running cost is flow temperature. A boiler happily pushes 65 to 75°C water round the radiators. A heat pump running at that temperature will have a miserable SCOP, perhaps 2.2. Bring the flow temperature down to 40 to 45°C and the SCOP climbs to 3.5 or better. That usually means some radiators need upsizing, and any survey that does not include a room by room heat loss calculation is not worth the paper it is printed on.
Insulation matters too, but less than people assume. You do not need a passivhaus. Cavity wall insulation, a decent loft top up and sealed draughts are usually enough for a heat pump to work well in a typical Cheshire semi or detached house. Solid walled Victorian terraces in places like Chester or Nantwich are harder and need more careful design.
Hot water is the other quiet cost. Heat pumps heat a cylinder rather than providing water on demand, so a family that showers heavily will use a bit more electricity than the heating figures alone suggest. Legionella cycles, where the cylinder is periodically heated above 60°C, add a small amount too.
Running cost is only part of the picture. A like for like boiler swap in Cheshire typically lands between £2,500 and £4,000. An air source heat pump installation, including cylinder, radiator changes and controls, usually sits between £9,000 and £15,000 before grants for an average house, more for larger or more awkward properties.
The Boiler Upgrade Scheme currently offers £7,500 towards an air source heat pump for eligible homes in England and Wales. That closes a lot of the gap but rarely all of it. Whether the remaining difference pays back through lower bills depends heavily on the tariff you choose and how long you plan to stay in the house. On a standard tariff it may never pay back. On a good heat pump tariff over 10 to 15 years it often does, and heat pumps tend to last longer than boilers.
If your boiler is reasonably new and working, there is rarely a running cost argument for ripping it out. If it is on its last legs, a heat pump is worth serious consideration, but only with a proper heat loss survey and a clear plan for flow temperature, radiators and tariff. Do that and the running costs are usually a little lower than gas. Skip it and you will end up on the forums complaining that heat pumps do not work, which is not the fault of the technology.
On a standard electricity tariff it is roughly level with gas if the system is well designed. On a dedicated heat pump tariff it is usually cheaper, often by £200 to £400 a year for a typical Cheshire semi.
Usually some of them, yes. Radiators sized for a boiler at 70°C are often too small for a heat pump running at 45°C, and a heat loss survey will show which rooms need larger ones.
Yes. Modern units work down to minus 15°C or lower, and Cheshire rarely gets close to that. Efficiency drops on the coldest days, but the annual average is what determines your bill.
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