God knows I promised myself I wouldn’t write anything about us having fitted heat pump. But having recently found that I can’t go online without seeing various strongly held opinions, such as:
- Heat pumps are a scam (see also global warming, net zero, blah blah)
- Heat pumps don’t work in anything other than a new build house
- Heat pumps make a really loud and annoying noise
- Heat pumps are entirely unsuitable for use in the UK
.. and while I know some of these are in bad faith I felt compelled to chuck my two cents out onto the internet for anyone who cares: we replaced the combi boiler in our (1950s, three bed, end-terrace) house and it has worked boringly well, even when it has been bloody freezing outside. Also, I mean, just look at it. Industrial design? Nah, just a beige box.
Where We Started
We live in a house, end-terrace, built in the 1950s as social housing in SE London. It’s a brick cube, with cavity walls and large air vents in just about every room.
We had already fitted double-glazing, and the loft was insulated (but not terribly well). Our EPC was a D. The heating was from a gas combo-boiler, about 15 years old and on its last legs. Radiators were an odd mix, including some that were really old and beginning to rust.
With the gas boiler and a Nest thermostat, the house could – just about – be heated to 19 degrees without burning a huge amount of gas. I would not describe the house as having been warm – it was OK.
Preparation
First, we knew we needed to insulate. We had cavity wall insulation – blown fibres, not beads – fitted into the cavity walls, and at the same time had the unnecessary air vents blocked. Only the bathroom retains a vent, for the fan, while all other rooms have ventilation via trickle-vents in the glazing.
With that done, we updated our EPC, and received a C rating.
Since we would be removing the boiler, it seemed daft to keep our old gas hob in the kitchen – taking out the gas entirely would mean no standing charge. So I had a plumber disconnect that, and replaced it with a plug-in Induction hob. I was thinking of this as a stop-gap until we could get the kitchen wired for a higher power one, but actually it’s been absolutely fine in use.
Rooms and Radiators
A key part of retro-installing a heat pump system is ensuring that you have adequately sized radiators. The radiators in our house were a mess – a hodgepodge of sizes and types, which kept some rooms hot (the kitchen) and left others chilly (our bedroom).
We had Octopus Energy quote us for a pump. They surveyed the property – in fact, they surveyed it three times, for reasons that I never entirely understood, and this was a bit annoying. But: at the end, a plan was produced to replace every single radiator in the house bar a towel rail in the bathroom.
A key lesson here: check this plan very carefully. Ours included a downgraded radiator in one room that was already cold, and an absolutely monstrous one that would pump heat out into a lean-to that we use for storage. I queried both, resulting on the cold room getting a bigger radiator and the lean-to being relegated to “non inhabited” and unheated. This also reduced the pump spec from 9kW to 6kW.
Annoying-and-boring stuff
I want to be honest here and note a few things that were annoyances during the planning phase:
- The aforementioned three surveys. Who knows what that was about?
- We needed to install a water tank in the loft. Our house was built with a water tank in the loft, so that shouldn’t be a problem – but nonetheless we had to commission and pay for a structural surveyor to give the OK.
- The surveyor required a large metal plate – 50kg of steel! – be placed under the tank. Octopus declared this to be our responsibility, so I had to acquire one. I felt bad for the guy who delivered it.
- At one point we were asked, repeatedly, to pour a large concrete base for the heat pump. It does not need a large concrete base. In the end, sanity prevailed here.
The Install
The installation took a week. We were without central heating for three days, but never without hot water overnight – the water tank went in first, and we used the backup immersion heater built into it for a while.
Every radiator in the house was changed, other than a towel rail. The new ones are very boring, very white, and work very well.
By the end of day 4, the pump was commissioned and heating both water and the radiators.
You control it via a wall mounted unit – which is pretty crap – or an App, which is boringly functional. But once I had set a schedule that works, I’ve just left it alone to do its thing.
The Results
Since first turning it on, the pump has kept the house at a steady 20-21 degrees without any problems whatsoever. It’s running on a schedule, based around the Cosy Octopus electricity tariff, to heat water twice a day if needed and to hold the house above 20. I haven’t even really had any excuse need to fiddle with the controls.
Costs: it’s very hard to do an accurate comparison. But as an example: in a 4 week billing period from Feb-Mar 2024 we were spending £3.75 per day on Electricity, including standing charge, and £3.40 on gas. Over the same four week period this year, we spent an average of £4.08 per day plus £0.35 standing charge, no gas. Obviously we’re using a lot more electricity than before, but this is concentrated in the cheaper time periods so our average cost per kWh is around 20p.
We haven’t yet run the pump through snow and ice – but it kept the house and water warm on some sub-zero nights with frosty mornings. Most of the time the pump is running, it draws less than 1KW. The immersion heater has been running exactly once a week for the legionella cycle. The 180l tank has been fine for three of us.
As for noise – you can’t hear it inside the house. If you go and stand right in front of the pump, at night, it sounds like a large fan running. If you’re lucky to be living in a bucolic wilderness where you can hear the sound of a butterfly’s wings outside, noise might be a consideration – but we live in South London where traffic noise exists, so it really is a non-issue.
All told, the heat pump install – including radiators, and after the £7,500 rebate -cost us in the region of £3,500.
Boring Advice
If you have a perfectly good and recent boiler, I would not rush to replace it with a heat pump unless you particularly want to immediately reduce your carbon footprint and have plenty of spare cash to spend on that.
If you have an old boiler that will need replacing soon, I would absolutely look into it. The results are boringly fine, the costs are boringly fine, and you’ll be reducing your dependency on fossil fuels in a significant way.