Perfect, so a £5.5k difference on that before the grant, which could arguably come down if paperwork requirements were less … great example
I’ve added your systems @simon_sh @Rachel @gm0705 @steveconuk but not sure of all the values to complete the entries. @steveconuk what do you think is your SCOP and annual electric consumption?
heatpump_costs2.ods (26.7 KB)
It would be interesting to get more examples of boiler vs heat pump costings, both boiler replacements and costs for installation of new boiler systems including radiators and pipework.
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Daikin 4 KW system.
Hopefully the information below is the information you require.
SPF based on MMI 3.65
Elec for Heating and Hot water 1151 kWh
Heat required based on survey data 4202
This is my first winter with the system, I am still learning the ropes.
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My rental properties all have modem radators as CH heating installed within last 20 years, my home is likely 40 year old radiators/pipes. So when gas boiler in rentals need replacing it can be a simple like-for-like swap done with one day labour, likely pipes will need no changes if keep to same make.
Radators in my home will be replaced when removed to do other work if not allready replaced for other reason.
FWIW, there’s an article at Heat Pump SCOPs – The Truth Might Not Be What You Think - Renewable Heating Hub based on data from https://heatpumpmonitor.org/
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Disagree about the alternative DHW mechanisms (solar PV etc), its just skewing the stats rather than enhancing the HP.
Economically it doesn’t make much sense either for SEG users, 15p export and overnight 7.5-12p divided by 2.5 COP is cheaper than diverting during the day etc.
The lack of ground source representation in the top 20 is err a lack of ground source representation in general 
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Hey
I think you might consider calculating the Levelised Cost of Energy (in this case for heat).
This is comparable to gas/oil etc.
It’s the metric that professionals would use when comparing electricity generation costs between technologies.
I’ll reach out to Lewis - happy to show you how to add it to the spreadsheet. Likewise if you want some help adding to some of your open source code let me know.
Then you’ll need to depreciate assets at different rates - one assumes a heatpump has a shorter shelf life than new oversized radiators for example.
I’m working on doing these calculations using 80 years of hourly weather data in an upcoming app. That’s beyond the scope of a spreadsheet or PHP but will cointegrate with solar simulation.
Best
Ben
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Thanks @kilowatts.io, it would be great to have your input on improving the calculation model, cheers!
Air Source Heat Pump direct replacement for oil central heating boiler - the payback can be very different…
This year I replaced my 25 year old oil fired central heating boiler with a Samsung 8kW Mono HT Quiet as a direct replacement reusing all the existing plumbing and tanks. I would be interested to know if anyone else has tried it. Running at slightly higher temperatures may be less efficient but it is still be much lower cost than heating oil. I found the low cost, ease of installation and the much reduced disruption made up for the loss of the boiler upgrade scheme.
The house is a 4 bedroom detached brick built in an exposed location in the south of England dating from 1890 with a modern extension. It is fully double glazed with loft insulation to around 300mm and cavity wall filled in the extension only. I would need to upgrade wall insulation for a BUS grant unless I could argue the old building is not suitable. The MCS certified quotes wanted to replace the DHW tank with a plant room and all new pipework to give the guarantee and the quotes started at £15k.
To test the suitability of my heating last winter I set my 18kW Wallstar boiler to 48C flow temperature. Set like this the daily fuel use on the coldest day was 12 litres. The 25 year old oil burner never quite reached the 18C house target temperature in all rooms on sub zero days but it was comfortable enough with the log burner when really cold. I was using 1500 litres of heating oil a year at a cost of £1200 at 80p/litre. From this trial I calculated the peak heat loss.
The replacement ASHP reused the existing indirect DHW cylinder and all the pipe work reducing costs and labour. I made no changes to the radiators except to fit fans to two radiators in the kitchen and living room. I did not fit a buffer tank. A Samsung approved speed controlled Grundfos pump was fitted in place of the old one. All the existing pipe work is 15mm minimum with 28mm to the DHW tank and whilst old it is all still in a good serviceable condition.
The Samsung supplied controller was wired up and set to use the LCD wired room thermostat with water law settings 15c,-5c : 35c,48c. All other settings are as factory. The consumer unit wiring needs to be completed and checked by an electrician. The header tank was flushed, filled and checked for leaks. The system was then switched on to test. After few minutes the new Grundfos pump started, the controller booted up and the heat pump started working first time with no fault messages.
The first test was to select DHW and it reached a 60 degree flow temperature in about ten minutes and heated the existing tank to a 45 deg C in 60 minutes. The COP based on the display was 2.4 so cheaper than heating oil when using Octopus Cosy tariff.
I opened all the thermostatic radiator valves and zones and found that with a flow temperature of 38C it keeps the whole house at 19 deg C with typical outside temperatures of 10 deg C. The COP is estimated at around 4.
I had to wait for freezing days in November for a real test. Temperatures were below zero all day with snow on the ground, and the heat pump performing the defrost cycles every hour or so. The flow temperature rises to 48deg and all rooms were achieving 18C. It is clear that you must run the ASHP continuously for this comfort level. I never turn it off but there is a set back temperature at night. Comparing oil of 12 litres a day maximum for the space heating and DHW I now use 40kWh and the COP is 2.5, at my average unit cost of 18p the daily cost is £7.20 compared with £9.60 for oil on the coldest days, i.e 25% cheaper. The comparable running costs will be even better on milder days due to the improved COP.
I found it was an easy job for anyone with plumbing knowledge but it does, of course, require a qualified electrician to complete the wiring. The official manuals are rather over detailed and difficult to understand but Midsummer Energy Ltd supplies everything you need and has a good summary of how to install this type of heat pump. Any qualified plumber could do this work. I notified the DNO on line after installation and there was no problem getting the approval to connect. In my case no planning consent was required provided I followed the local planning guidelines and building regulations.
Manufacturer’s guarantee may be affected if you do it yourself, of course. I registered for the extended warranty with Samsung on line as there may still be some recourse if a manufacturing defect is found at a later date. Samsung UK will respond if you need help with their products.
There are 1.5 million homes with oil fired central heating in the UK. If the pipework is serviceable with an indirect DHW tank then they could benefit from ASHP without needing to replace the internal plumbing systems. For my simple installation example the additional costs of ASHP compared to a replacement oil boiler can be expected have a payback of less than ten years even without the BUS scheme and MCS certification.
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Thanks for a great write up. Whats the dt between flow/return when heatpump working hard?
Two thoughts.
What about a basic A2A in the living room to use when very cold?
If the money saved on radiators was spend on a home battery (eg one or two Fogstar 15kw) and a tariff with a low overnight rate used, what would running costs be?
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Glad you found it interesting. I do not have reliable return temperatures readings but will check it out when I fit some monitoring. I will likely increase the size of radiators to improve efficiency in the future but right now it works OK.
I have a log burner to use when it is very cold in the living room so that works for me but A2A is always an option.
Interesting you mention batteries because I already have 7.2kWh of battery storage as part of my solar installation. I do use these batteries to make full use of the off peak tariff, two full charge/discharge cycles a day on cosy Octopus is worth around a £1.40 a day to me so it is definitely worth doing.
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Apologies for very late set of info!
My HP install was done under the HeatGeek assured scheme, with design consultation in Feb 2024, installation June and commissioning July. Previously had gas combi, which for the period July-December 2023 was already running mostly at 50°C flow temperature with 3rd party controls and weather compensation. For some of the time heating on 24/7 with an overnight setback. It was a period of tinkering.
Design consultation: £350 (inc VAT)
Heat Geek guarantee: £500 (this was reduced from a higher figure due to problems with the website and Heat Geek design tools which I reported)
Parts:
- Heat pump: 7Kw Vaillant Arotherm+ £3806
- HP accessories, sundries, electrical parts (inc new consumer unit) £2635
- Controls: Vaillant sensoCOMFORT (Wireless Controls) plus gateway £435
- Cylinder: Vaillant uniSTOR 200L £1014
- Radiators (5) and valves (12) £1188
Parts Total £9079 (no VAT payable)
Labour:
- General, including moving around an additional 4 radiators £5656
- Heat Pump Monitoring Level 3 £300
Labour Total £5956 (no VAT payable)
Additional work post installation - plastic pipework replaced with copper (parts and labour) £655 inc VAT
Level 3 Heat Pump Monitoring Bundle £942 inc VAT
Grand Total to date £10132
Target temperature of 18°C.
Heat Geek Estimated system efficiency: 380% efficiency at 45°C max flow temperature
HOUSE LOSS 7.99kW
ROOMS 11 Total
EXT. TEMP. -3.0°C
The heat pump has been installed and running for 6 months. Early heat metering errors appeared to have disppeared, but some more reported recently (only thing that’s changed is defrost cycles…)
Heat losses were calculated on the assumption that underfloor insulation would be installed - it still hasn’t happened, and ground floor less well insulated than a year ago!
Heat loss for loft bedroom greater than modelled, and waiting for an even bigger radiator (will have to pay for radiator, but not labour).
Heatpumpmonitor space heating stats for July to December:
- Electricity: 1593 kWh
- Heat: 6995 kWh
- Mean Flow temp: 29.4°C
- Heating COP: 4.19
- Mean Outside temp: 8.6°C
- Mean Inside temp (first floor N facing bedroom): 19.6°C
I switched from the Octopus flexible tariff @ 22p/kWh for electricity to Agile in mid September (I also had the gas meter removed around the same time)
I’ve quickly checked Octopus bills (last 3 weeks of December 2024 from Octopus Compare). Combined gas and electricity costs for July-December 2023 appear to be £690 (tracker for gas, flexible for electricity, while for July-December 2024 they appear to be £680.
16°C degree days for July-Dec 2023 is 827, while for same period 2024 is 846.
So not a huge difference over thoise 6 month periods.
Subjectively the upper floors of the house are warmer, while the ground floor is cooler. The ground floor is less well insulated than it was in 2023, and draughtier (improved underfloor ventilation, all ground floor coverings removed, and parts of boarding also removed), and I’m confident that things can only get better when the insulation and airtightness issues are resolved and implemented.
Finally I managed to sell the combi boiler (only 7 years old) to someone who needed one to see him and his family through the winter while renovating a property before installing a heat pump!
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With a large lounge like that with 3 solid outside walls you may want to consider insulating those walls. Insulating inside and outside are both very effective. Outside is quite expensive and a specialist job.But inside much cheaper and easy to do for a competent DIY person with advice from your council Building Control office who will issue a certificate on completion. You do lose a bit of external space but not noticeable on a room that size., I used 50mm PIR foil faced boards held on the wall by 25mm roofing laths spaced 400mm. 12mm plasterboard goes on top of that. so you lose about 90mm. The 25mm air gap increases insulation as well and is useful for routing cables through. U value goes down to somewhere around 0.3 from around 1.8 so the saving on heating is considerable for a relatively small outlay. You can do it one room at a time so minimal disruption. It beats crawling around under the floor by a mile unless you are a pot holing enthusiast.
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Heat Pump running cost sensitivity analysis.
I now have a years worth of data for my system and have produced a spreadsheet to try to understand the cost drivers and which levers to pull. From the outset I considered the heat pump/solar/storage as an integrated system to make use of the lowest available TOU tariff.
The running costs…
My annual bill last year was £1737 including charges. The TOU tariff is Octopus Cosy for the heating season and then Go in the summer season. This running cost is less than mains gas heating for my UK detached 4 bed Victorian house, mostly well insulated, heated to 19 degrees for 19 hours a day. We do use a lot of hot water which pushed up the all year round baseload to 16kWh a day.
The attached screenshot shows all of the inputs required that affect running cost - it is a long list…
note how the coldest months are £300, a bit of a shock if you do not know that is coming! In the summer the costs are mostly just standing charges. The battery works hardest in winter cycling twice a day so that heating is on continuously at the cheapest rate and never at the peak rate 4pm to 7pm. The average rate over the entire year was 16p/kWh ( the summer go tariff at 8p is used to the maximum when there is no solar).
But what if I just installed a heat pump?…
Had I not installed a battery I would have to resort to scheduling to avoid expensive TOU tariffs. This is difficult to do and still be comfortable, even with triple dip TOU. I assumed you can move 50% of the demand and still keep the comfort. The result is £2883 per annum or 22p/kWh.This is an increase of £1146 over the year, or a 5 year pay back on the solar inverter battery combo.
The most expensive option is the battery storage but the savings are nearly as much as solar and will just get cheaper over the years.
Here is just the 8kWh battery storage option and it gives £2329 annual running costs with a saving of £554. Again a 5 year payback.
My domestic heat pump system is 8kW rated but it can reach 9.5kW, my heat loss is 8.5kW at -1C. It comprises a SamsungHTQ heat pump plus 3.6kW solar panels with hybrid Solis inverter and 10kW Dyness (8kW usable) storage. Solar cost was £2500 partly installed by myself on a ground floor garage roof. The battery would normally be £2500 but I bought used ones for half the price. The Heat pump and pipework was around £6k and again I did most of it myself using an existing DHW tank and did not apply for the grant due to delays and conditions. The grant would probably cover the labour if not doing it all yourself say £17.5k total. I know many people are quoted far more but all properties are different and mine was a straightforward conversion. It replaced an oil fired boiler with annual energy costs of both electric and oil of nearly £3k annually so a no brainer really…
The saving over oil is £1.4k annually making the payback 12 years. There is no payback on mains gas unfortunately but as the above shows if you are paying much more than 22p a unit for electricity on average it may be worth getting battery storage especially if you already have a suitable solar inverter.
The availablity of low cost TOU in the future is always a concern as many consumers take up the option making them more expensive.
It is a very complex subject. My spreadsheet may be wrong and I apologise in advance if it has errors but I would be interested to know if these annual running costs seem plausible from your own experience…
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Excellent information.
My first winter with a 22.4kw cascade system.
House is 306m²
9”solid brick walls. House EPC is a B.
Gas usage last year was 34000kwh. That’s with a max rad temp of 50c. House set to 20c. 74% efficient worcester 40cdi set to max output 13.6kw last year.
Looking at October / November bills compared to last year’s bills, I’m saving 50% so far.
I do have 9.24kwp solar and 10kwh solaredge battery. I’ve had the system for 3 years. I have 5 years left until the solaredge system has paid me back.
I’m on Agile, as cosy tarrif iis expensive in the Northwest. Im using predbat to automate battery state of charge to maximise cost return. Works well. As cosy it’s fixed I don’t think there would be much of a cost benefit. I’m running predbat on a pi5 which is free but there’s a paid version if you don’t want to mess with home assistant. There’s limited systems that are supported if you pay for predbat. At the moment solaredge isn’t available.
One big savings that I’ve not accounted for was the reduction in the use of the log burning stove. This reduction will be partly because I insulated the ground floor crawl space with ybs superquilt. 116m².
I do setback 1c between 4pm and 7pm. This will be the only time I’d need to light the stove.
So far the 10kwh battery has been just enough to cover load over peak hours.
As its mild only one 1 ASHP has been ticking over. Max I’ve used in 24/h is 24kwh. This includes heating DHW once in 24 hours.
Thanks.
Another data point:
4-bed Victorian semi, ~145sqm, mostly uninsulated solid brick walls. New ground floor extension and loft insulated to current regs. Edit: measured heat loss is ~5.5kW at -2C outdoor/21C indoor design temps.
7kW Vaillant Arotherm Plus. No solar or battery.
Whole house kept at 21.5C 24/7/365, no setback. 250l DHW tank reheated daily.
Total cost for all heating and hot water for the last 12 months: £390.
This was with Tomato Energy, who have now gone bust, so will increase over the next 12 months…
Thanks for that information. I am particularly interested in annual bills paid for a given heat loss property across the country, especially when a heat pump is the only source of heating.
The average energy costs for a UK property on mains gas is currently around £1800. Typically halve of this is heating and DHW and the rest is cooking, washing, lighting etc. I am trying to see if our community of heat pump users are at least matching this.
I do not think it is currently possible to have a payback on the costs of electrification of UK mains gas homes, without also fitting solar panels and improving insulation, due to the current electricity costs- it seems the payback calculation is all about the TOU tariff and how you manage demand.
The simple calculation is that UK mains gas is 6.29p and the likely best heat pump SCOP is 3.5 so the average annual tariff paid must be less than 22p or you will have to compromise on heating comfort or have additional heating like solar or wood burner or more insulation for example.
PS I see that there is already a table of more information higher up in this thread that could have total energy usage added such as…
| Total energy purchased for the year kWh | |
|---|---|
| What proportion is Heating and DHW kWh | |
| Cost of all electricity for the year £ | |
| Average rate paid for electricity year £/kWh | |
| Tariff used during the year | |
| hours per day heating | |
| Avg room temperature achieved throughout | |
| Heat Loss of the building kW |
TrystanLea, The UK government is targeting a break from gas setting the UK electricity price by 2030. The spark gap should, fingers crossed, be much better (around ~2.5) than it is presently (~3.5). If the plan succeeds, then it effectively allows no need for extra batteries or solar and would potentially allow radiators at 55C. So maybe no radiator upgrades! This is the situation in Spain. The market is not replacing radiators, but running hotter with cheaper electricity than the UK.
Unfortunately, the economics of such a change would require a ASHP payback period still measured in many years. I expect a the UK (MCS) grant will not be sustainable in future…..so expect that to disappear. Most UK homeowners would not pay ~£10000 with no subsidy for a heat pump, if a gas boiler was £2500. The cost difference is too big a horse pill to swallow, even if the payback period was in 10 years.
I hope the heat pump manufacturers or energy suppliers start to recognise a need for leasing or finance packages in the near future (2030), knowing the heat pump payback is ~ 10 years with a lower spark gap ~2.5 and likely no BUS grant.
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Hi designerguy, I can give you the information your after in early January 2026. However, it is for Northern Spain. Honestly, it does get chilly here for a few months of the year. It may be of interest to you because the spark gap here is typically lower than in the UK. So it may be the UK future in 2030 - if the government electricity decarbonisation plans play out.
If it’s of no value, then no problem.
Apologies, I haven’t kept up with this thread recently. I’m going to catch up over the holidays 
There is now an option to enter the installation cost (before subtracting the grant/subsidy) on HeatpumpMonitor. It would be amazing if we could get a few more installation costs on there as there’s only a handful so far. @glyn.hudson and I cant add ours as both of ours are self-installs and so the costs are not comparable. Make sure to add the actual cost of the install before the grant:
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