Are heat pumps any good?

Is it worth getting a heat pump?  Is a £1,000 mini-split a heat pump?  Does Liz Truss know? Who is Liz Truss?

Heat pumps in theory will save the world. For each unit of electricity they use they move about 3 units into your house. However, most of us live in houses that are already built (best kind to live in if you ask me) and not designed for heat pumps. You can see a discussion about heat pumps and radiators here – Radiators and heat pumps – but basically your house is almost certainly not going to work well with a heat pump unless you already have underfloor heating, fan coils or a passivhaus build. Otherwise, you’ll need to almost rip it apart and start again.

Heat pump power

What are the snags?

Apart from the radiator issue there are other integration snags. If you have a combi boiler there is no hot water cylinder but the heat pump will be too weedy to heat water on the fly so a tank will be needed. If you have a hot water cylinder already don’t be too smug. The coil in the tank is designed for very hot water from a boiler. Heat pump cylinders have much bigger coils so you’ll need the upgrade. In practice these tanks usually need a daily boost from an immersion heater which runs on the most expensive energy source you can buy.

So, it’s not just the cost of the heat pump; the new tank etc is very likely to push the cost to circa £15,000. (£5,000 from the Government so make that £10,000).

Assuming you are still up for it you might want to study this chart of current (winter 2022 Truss revision + Sunak) energy costs compared.

Here you can see that the cost of running the heat pump compares well with natural gas, oil, lpg and wood so the cost of running it won’t be too bad – or will it? Wholesale electricity prices are literally around double the artificially fixed price on the chart so for how long do you think those prices can be subsidised?

It seems to me that you can buy an awful lot of gas for £10,000 so why not stick to a nice powerful and cheap gas boiler while you can still get one.

Ah but I’ve got solar panels

Good for you. And if your array is big enough then a heat pump is the way to go. If we all had a big solar array and a heat pump the energy crisis would be over. It has to be a big array though because on a short winter day the panels lose their sparkle to a large extent and then quit altogether by tea time. Batteries step in here but they are unlikely to make financial sense unless you get them free in a leased electric car and don’t pay for their degradation – all that is another story for another day.

Moving away from the big money discussion let’s talk about mini-splits. Just like air source heat pumps in this note they are proper heat pumps but they are air to air so they blow hot air into the house. With no connections to water they are quick and easy to install and only about £600 odd to buy. As part of a hybrid solution one of these makes so much sense that the Government should incentivise them along with a bonus if they are paired with solar panels. At least this is something most people actually can do, rather than something that they should do, but can’t.

Here’s one I installed in my house paired with a 4kW PV array.

What’s it like?

The panels run it for free on most days of Spring and Autumn but not in the depths of winter although it is so cheap to run that it regularly dries the laundry by blowing hot air over the drying racks. In Summer the air conditioning is a big bonus as the cold air spills across the whole house and on a hot day electricity is always free.

The whole cost was under £1,000 fully fitted in just 4 hours. You might consider one with more than one indoor unit or another completely separate one. A pair of these would work well with solar panels – you could run both when the sun is out or just one on a cloudy day. Free heating should be enough to keep the old gas system switched off and when the sun is stronger the immersion heater will make your hot water. On dark winter evenings the choice is yours. Mini-splits and gas both cost about the same to run per but the splits let you do more localised heating at less cost. So, to sum up. £2,000 not £10,000. Non disruptive installation. Works with your legacy system. Air conditioning. Some free running with solar panels. Dries the laundry really quickly.

During the last big freeze I avoided any burst pipe stress by running the split all night – dried a load of laundry at the same time

N.B The £8,000 you saved by not having a regular heat pump would buy a 20 panel – 8kW car port!

The difference between this and a £15,000 air to water system is so massive you’d think the Government should take note. Feel free to forward this to your MP if you agree.

My note on Radiators and heat pumps gives some essential clarity on heat pump issues. If you didn’t click through earlier I’d urge you to do so now.


3 thoughts on “Are heat pumps any good?

    • ABSOLUTELY RIGHT .. A few panels and a mini-split is the biz though…. mine seems to draw about 300W a lot of the time so the panels cope very well…. not much left over after the Eddi feeds the immersion so a low powered mini-split works without too much stress.


      • Air to air makes a lot of sense. That’s why (like mixed air & ground source) it’s excluded from the BUS.


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