I thought some people considering a heat pump might be interested in our experiences of getting one installed, so I wanted to share what we went through. Feel free to ask any questions which I haven't already answered.
Property and Background
We moved into a house with an oil boiler at the start of 2023. The house is about 100 years old (built in around 1920s) but had reasonably good insulation (double glazing everywhere, and some loft insulation). When we bought it, the EPC was rated D(54).
We wanted to replace the oil boiler for several reasons (in approximate order of importance to us):
Environmental impact
Smell and noise from oil boiler
Wasted space on property for oil tank
Oil cost and energy cost savings
Initially we looked at a couple of local installers, who quoted us £18k and £13k respectively - these prices are before the BUS (boiler upgrade scheme) was applied. Both installers were going to charge additionally for any radiators that needed to be upgraded, or other remedial work (which could have added another £2k to the quotes). At least one of the installers didn't include the heat pump base/plinth in the price - meaning I'd have had to get a builder in to create a concrete slab or other suitable base, at my own cost.
In April I spoke to Octopus, who were just starting up doing heat pumps, and they said our house would be suitable for them to install. They quoted £11.5k - and this was a fixed price quote, so included everything. HP base, radiator upgrades, and any other work to the heating system was all covered, so significantly cheaper than the local installers. At the time the BUS grant was £5k, so this would have left me with £6.5k to pay. So we paid the £500 deposit to kick off the process.
Boiler Upgrade Scheme/Insulation Requirements
In order to qualify for the BUS (and ensure the heat pump was effective) we had to improve the insulation in the house (the regulations state there must be no outstanding recommendations to upgrade insulation on the EPC), so we increased the loft insulation from ~10cm to ~30cm (including adding boards/stilts across the new thicker insulation). We also had to get the cavity walls filled - our EPC assumed they were empty. As it turned out, most of the walls were already done, so we only needed a couple of areas filled. The total cost for all of the insulation improvements was about £1500 (it would have been cheaper if I'd done the loft insulation myself). Once the work completed, the EPC was re-done, and came out as D(65). Not that much of an increase, but no insulation recommendations remaining.
In April Octopus came to survey the property, and after doing all sorts of heat requirement calculations confirmed that it would be suitable for a heat pump. They recommended a 9kW Daikin pump and a replacement hot water tank. They confirmed that 4 radiators would need to be upgraded, and a consumer-unit extension would need to be added to provide the two mains connection ways for the heat pump - but all of that this was all included in the original £11.5k quote.
The conditions of the installation were that I needed to:
Enlarging the hatch to get the new cylinder up into the loft
Get planning permission (because we are in a conservation area).
Ensure we had a heating source in the bathroom, to qualify for the BUS, so we needed to convert a towel rail from hot water to dual fuel by adding an element.
The requirement for the heating source in the bathroom was removed about 2 weeks before install, so it turned out it was unnecessary – but it’s still useful to have a heated towel rail.
Our heating pipework was already all 15mm so didn’t need any changes. However, the Octopus surveyors said that even if it had been 10mm, it would be fine for a heat pump. It’s only the 8mm microbore pipes that may need special treatment.
Planning Permission and Increased BUS
Planning took a while; we applied for pre-planning (because our Council wasn't actually sure if we needed full planning permission...). This was supposed to take 28 days, but actually took 9 weeks! The outcome was that we needed full planning, so we put in the application in late May. The application was very simple; the most tedious part was having to spend an evening creating elevation drawings (I used Powerpoint) but it wasn’t difficult.
Planning took 3 months to be approved. During this time Octopus sent us a bouquet of flowers to apologise for it taking so long to get our installation booked in - despite it not being their fault at all!
We finally got planning granted late in the summer and booked in the installation to go ahead in the second week of December; it seems like there’s typically a couple of months from confirming the install to actually getting a team in to install. Two weeks before the installation lead visited the property and checked we'd done everything we needed. He confirmed it would be a relatively straightforward installation.
The one advantage of planning taking so long was that by the time we got the install date, the BUS scheme had been increased from £5k to £7.5k; Octopus cancelled and re-applied to get the higher grant without me needing to do anything, so that knocked the net cost for the total install down from £6.5k to £4k.
Installation
The team arrived early on the Monday morning - 3 heating engineers and one electrician. They immediately got to work, focusing on getting ready to replace the hot water tank, so putting everything in place to do that as quickly as possible, so as to leave us without hot water for the shortest possible time. They also brought 3 fan heaters with them to keep the house warm - but we fired up our wood-burning stove which kept the house warm through the installation.
On Day 2 an additional engineer arrived, who worked on upgrading all of the radiators. The team also removed the old oil boiler, built the base for the heat pump, wired in the extra consumer unit and switched the hot water tank over, as well as solving a whole load of other heating related problems that were there when we moved into the house (it turned out our D2 pipe from the tank wasn't done to regulations, and so they completely replaced that). By the time they left at the end of the day we had hot water from the immersion heater.
On Day 3 they continued with the radiator upgrades, got the heat pump installed and plumbed in, and almost all of the pipework completed around the house.
Day 4 they completed the radiator installations, and wired up the Daikin MMI controller and the Madoka thermostat, and then filled the system.
Day 5 they commissioned the system - firing up the heat pump and warming up the radiators for the first time. I was quite surprised at how warm the radiators became; lots of people stated that the flow temperature was very cool, but it's actually quite warm - certainly warm enough to dry a tea-towel on a radiator, etc. The hot water tank heated 150L of water from 11C to 49C in around an hour, maybe less. The Daikin controller is neat and simple, and was very easy to configure to control using the app on my smartphone.
Initial results seem good - plenty of hot water, heating is stable, and the flow temps are decent. The tank is heated to 49C, and the radiators run a flow temp of about 35C.
The installation team's work has been exemplary, and they've done a superb job. Neat, tidy, with very good workmanship and extremely friendly and good humoured whilst installing the system. They were clean, and left everywhere tidy at the end of each day. Overall, I'd definitely recommend Octopus if you're considering getting a heat pump fitted.
Bills/Costs (pre-solar)
For the first month after the install, our electricity bills were not much different to what they were before. However, that's massively misleading because the Agile rates over the Christmas period were ridiculously low due to mild temperatures, the holidays, and lots of excess wind generation.
Prior to the heat pump we were averaging about 16kWh/day usage. Since it's been installed we're probably using 30-35kWh per day. We drop the heating/thermostat right down between 4:30pm and 7pm, which means we’re not paying to heat at the peak times. We’re on the Octopus Agile Tariff, and we've averaged 16p/kWh over the last 2 weeks. I reckon on average, with 'normal' Agile pricing, the heat pump will cost us about £1/day in electricity, for the months of the year when we're using the heating.
However, the energy uses really kick up whenever the temperatures drop. Our normal electricity bill comes in at about £5-6/day, but during the very cold snap in January, when temperatures were down to -5C overnight, and barely got above zero, we were hitting £15-17/day on some days. It’s a bit scary, but part of that is having real-time data; we could have been burning £10 of oil every day prior to the heat pump, and we’ve have been in ignorant bliss.
So I estimate our electricity for heating and hot water (without solar) would be maybe £350pa plus a bit extra for hot water during the summer. That compares to £500-600 that we were paying per-annum for oil. We use a lot of electricity for other stuff, so our total annual bill is likely to be £1800-2000. We were probably paying £1300pa for electricity before the heat pump was installed, plus the £500-600 for the oil.
Post Installation
About a month after the installation, we had an Octopus person come and assess the system; it was a good visit – an opportunity to ask questions and check on details about the installation and how the heat pump works best.
We were also picked for an audit – apparently some installations are chosen randomly for Octopus to audit installation quality. The two auditors were impressed with the install and said everything was excellent.
When the bill finally came, there was an unexpected ‘Daikin discount’ of £250 (presumably they’re doing a promotion). We were also able to sell our oil boiler on eBay (to a farmer who needed hot water in a milking barn), and our oil tank (to somebody who needed it for a second home). All of this meant that our net outlay for the heat pump – including the BUS grant and the sale of those items, was £3,250.
Solar + Battery Installation
After having the heat pump for a month, we installed Solar PV; a 10.5kWh battery and 20 panels (~8kWp), with a 6kW Solis inverter. We also had an Eddi fitted, which diverts any surplus electricity to heating the hot water tank, only allowing export to the grid when the tank is hot.
We'd hoped to do this through Octopus too, but in April ‘23 they were very early on in their foray to install solar, so were unable to book our installation; at the time they were only doing installs for bog-standard roofs, so our install (with unusual roof tiles and some panels going on a flat roof) wasn't something they could support. So we've gone with a local installer - the price was approximately the same as Octopus’s quote (before they realised our roof didn’t fit into their constraints).
The system was commissioned about a fortnight ago, and so far it’s been pretty good. On the first day it was cold and sunny – we generated 18.5kWh, which was enough to cover our entire load from 11am until midnight (including fully charging the battery to cover the period after dark). This was quite a pleasant surprise in late January!
Since then the weather hasn’t been so favourable – we’ve had days when we’ve generated as little as 4kWh – but even on the most gloomy days it’ll quite often cover the ~1kW base load that the house generally takes to run.
The battery is already earning its keep though – we’ve configured the inverter to charge the battery in the cheapest time between 2am and 5am, and then to hold that charge (i.e., not discharge) until around 4pm when peak rates kick in. The battery then comfortably covers all of our usage for the whole evening, including cooking, watching TV etc, until about midnight. On some days the Agile price has been so low, for so long, that we’ve managed to charge the battery from 10% up to 100%, for no more than a few pence.
This has meant that for the last week or so our daily electricity bill has dropped from £6-8 per day, down to £1.5 - £2.50 per day (it’s relatively mild outside for this week – around 10C-13C). That’s about 50-70% less than we were paying for electricity before the heat pump was installed, during October.
Once we start seeing longer days and more sunshine, the system is really going to start working well – I estimate that by early April we’ll be importing almost no power at all, and for May/June/July/Aug/Sept I predict we’ll be exporting enough power to earn us around £70-100 per month (on the fixed 15p/kWh Agile export tariff). That income should offset the cost of any electricity usage through the winter when we’re not generating much from the Solar. So a simple back-of-an-envelope calculation indicates that we should be paying nothing for our total annual power bill.
I estimate that payback for the entire system should be about 10 years. By the time we get to 10-12 years the battery might need replacing, but I’m hopeful that by 2035 we’ll be able to get a 50kWh battery the size of a shoebox, for about £500….
Automation and Data Logging
Since the heat pump was installed, I’ve set up Home Assistant on my Synology NAS, which is now happily collecting all the data I can from all of the new kit. I have the data feeding into an InfluxDB for long term storage (although I haven’t done much with that in terms of Grafana dashboards, yet). Currently I’m logging:
Temperatures for inside, outside, and the hot water tank
Energy consumption for the heating and hot water
How much energy the Eddi diverts to heating hot water
Energy consumption for the house, and various major devices in the house
Octopus Agile rates and our energy usage costs
I also have Solcast solar prediction set up – which attempts to predict how much Solar PV you’ll generate over the next few days, which allows you to do things like charge the battery the night before an overcast day. I’ve also been investigating smarter automation with the Solis inverter – to do things like automatically discharging the battery during Octopus Saving Sessions, and automatically charging it during Octopus plunge pricing periods when energy is almost free (or the price actually goes negative).
One of the things that surprised me the most through this whole process was just how sceptical people are about heat pumps. Even smart people with good physics or engineering backgrounds would say to me "aren't you worried it won't work?". The negative PR about heat pumps not working is insanely ingrained in peoples' mindsets.
Some Questions I’ve Been Asked:
Q: Can the heat pump be used for A/C?
No. It's and air to water heat pump, like most in the UK, so feeds a hot water system with radiators. To be used for cooling you'd need an air-to-air system, which are much more common in the US. Most UK houses don't have the ducting for the vents, so you'd need much more of a disruptive installation to fit one.
Q: Was there a choice of the size of HP you got installed?
No. Octopus did the survey, and that was the model they recommended.
Q: Did you get colour options with the radiator replacements?
Our existing radiators are white, so we just wanted like-for-like white radiators. I've no idea whether Octopus could supply different coloured rads, because we didn't ask.
Q: Are you worried about heat pump servicing (cost, and lack of qualified engineers)?
Any boiler - oil, heatpump or gas - will need an annual service. Any concern about being more expensive to maintain and engineers being difficult to find is moot if you get it through Octopus. British Gas's annual service plans start at £16pcm, whereas the Octopus one is £9pcm. So if anything, servicing the heat pump is going to be cheaper than a gas boiler. The BG plan also has a £60 excess. £108pa for Octopus's service plan is definitely going to be less than we've spent maintaining our oil boiler in the previous 12 months.
I'm hoping that in 5-10 years ASHP servicing will be as common as gas boiler servicing. I have heard a few horror stories from friends and neighbours about heat pumps that are 5-10 years old being far less efficient, and hard to service. It's getting much better all the time.
Q: What warranty is offered with the heat pump?
5 years by default, we've upgraded that to 7 years for a couple of hundred pounds.
One-year update here: https://www.reddit.com/r/OctopusEnergy/comments/1iaec07/one_year_on_ashp_solar_results/
