So many people are saying their new heat pump is costing a fortune to run. Well, they run on the most expensive energy available so what did they expect? This chart shows that heat pumps are no cheaper to run than gas boilers, so should you walk away from the idea right now?

Back to the chart though and WOW, look at that. A heat pump running on off-peak electricity will heat most houses for well under £1,000 over the 200 days of winter. So, no, don’t walk away; a heat pump run intelligently can be the best solution by miles.

But where is your house on all this? You can get there by extrapolating from your existing bill. So, say you spend £1,330 on gas (adding another third to that Nat gas bar) you are using about 24,000kW hours which puts you in the yellow house. Looking up to the ‘off-peak heat pump’ line, the same amount of energy would have cost about £500. The conclusion is that for any fuel and any house, a heat pump could halve your bills, but only if run on the cheapest electrcity.

How is that even possible? Well, it’s just simple maths. A typical small heat pump (12kW) consuming 3kW at 7.5p/kWh for 7 hours a night costs a mere £1.52. With a COP of 4 multiplier this makes 16,263kWh over 200 days for a mere £305. That would suit the small and well insulated green house. All this happens at night but we want heat during the day so now let’s talk about storage.The cheap energy has to be stored in water tanks (2,000 litres in this case) and there must be underfloor heating to use every last bit of energy in the tank. To get those cheap night rates you might need to have an electric car too. Any house better than the green house, Passivhaus maybe, will almost run for free. Going back to the yellow house, we’ll need 3,000 litres of water storage and a 17kW heat pump consuming 4.5kW at a total cost of £500. A fundamental point here; the heat pump is running fewer hours and needs to be unusually powerful to supply the energy total so it might need to be bigger than your supplier calculates.

The red house gets more interesting. 4,000 litres of water and maybe two heat pumps for an annual bill of about £600. For a deeper dive into all this have a look at the ‘Absolute ultimate heat pump system for large houses’. This explains how the system is put together along with some interesting enhancements.