Heatpump payback calculator (total cost of ownership)

Hardware Heatpump
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I started seriously looking at changing from gas to ashp about 2 years ago after I watched Glyn Hudsons excellent videos about his installation, which showed that it was possible to install a system which performed well. Tried to get some quotes, as I didn’t fancy grovelling in the loft to sort out the pipework, but most of them looked like ex double glazing outfits and the local Vaillant installer with a good reputation didn’t respond to my phone calls or emails. I got one quote from one of the double glazing firms which was £17,500 falling to £12,500 after the grant which was fro a Samsung 16kW heat pump, replacing 8 radiators and fitting a new cylinder.

Looked at that and though that heat pump’s too big and they’re just harvesting the £5000 grant as the components and labour shouldn’t amount to that much. I thought that I could probably buy the bits to do it for £7-8,000, including 20% VAT which the installer wouldn’t have to pay.

In the end I paid £16,000 for parts. (Would have been £12,500 without VAT and monitoring.)
Heat pump and controller £2,700.
New radiators £5,800
Ebay cylinder £480 (not fitted yet, still using the vented 120l one)
OEM heat pump monitor & 2 Samsung extras £940

Using standard electricity rates the annual saving would be about £210 or 71 years to recover the cost. Taking into account loss of interest that’s an infinite time.

We’ve actually moved to Intelligent Octopus Go which, in theory, will increase the annual saving to £1000, but the huge cost of the PV system and batteries nullifies that saving as well.

Things have changed since then and it could be possible to get a system installed for, at a guess, £8,000 but the payback time is still getting on for 40 years.

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Finally got round to my numbers:

Commissioning Date: 01/04/2022
Heat Pump: Mitisbushi Ecodan 8.5kW
Cylinder: none - have continued to use original cylinder with undersized coil as I have solar thermal and PV divert.

Heat pump + BoP: £4526
Fitting & MCS inc Electrics: £2026
3 x radiators + fitting: £ 824 (I’d previously uprated the bathroom rad when I had it redone 6 were unchanged from originals)
1 x radiator: £ 276 (fitted by me much later in entrance hall)
Civils (done my me): £ 100 (I guess that would have been £300 if someone else had done it)
Total cost: £7752

Grant: £5000
Net after grant: £2752

Annual Heat Output: 10,200kWh (heat meter), 11,469kWh (survey with no DHW)
sCoP operating flexibly on Agile: 3.82
Weighted average annual electricity cost for heat pump: 14.6p/kWh (be lucky to get that this year!)
Average heat unit cost: 3.82p/kWh

Rachel

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63

What an absolutely fantastic thread. Some really great stories and data.

This is timely because I have been looking at this for my own install recently.
I had a heat pump installed in Nov 2023 (monitoring from Feb 2024) and PV/batteries installed in June 2024. It’s hard for me to separate out the benefits of each of these. I live in a mid-terraced 1900s house with relatively recently converted loft, solid brick walls, crap double glazing. I estimated my heat loss at 5.5 kW, my installer (after much bullying from me) got his calc down to 6.5 kW. I twisted his arm and got him to install the 5 kW Vaillant Arotherm. The heat demand explorer suggests 4 kW is more realistic. All rads sized to 50 degree flow but in reality flow temp is in the range of 28-33, so rads are “undersized” to deliver the heat at that flow temp (but balanced out by them being oversized for the room actual heat losses). This culminates (I think) in getting quite a low delta T between flow and return - usually ~2 degrees. I hypothesize that the radiators cannot lose enough heat into the room at a flow temp that low, so the return temp is higher than it otherwise would be. Unsure if that has any impact on efficiency.

My heat pump install also included extract fan and induction hob installations.

  • EPC (needed for BUS): £95
  • ASHP + 200L Cylinder: £5,680
  • Plumbing labour: £5,500
  • 7no. Radiators + valves: £2000 (went for nicer rads than K2/K3 which only added a few £hundred)
  • Pipes, pipe fittings, fixtures, base: £1,890
  • MCS “piggyback”: £1,320 (grrr)
  • Elec materials: £780
  • Labour and materials for hot water cylinder cupboard: £1,290
  • Hob £150 (off Facebook market place)
  • Extract fan £250 (Vent Axia heat recovery fan, off ebay)
  • Metering/monitoring £710
  • BUS -£7,500

So say £10.5-11k for the base heat pump install all in inc grant and just over £12k including the nice-to-haves.

PV

  • 2kW of panels (max I can fit on roof) + 3.7 kW inverter + 9.3 kWh of battery storage, estimated generation 1,800 kWh/annum: £7,400

Call it £20k for the lot.

Comparing bills
Last full year
Nov 22-Oct 23 ~£1,220
Nov 23-Oct 24 ~£790
£430/annum saving = 47 year “payback”

Just the period which I have had PVs
Jun 23-Oct 23 ~£310
Jun 24-Oct 24 ~£100 (most of which is standing charge)
5 month saving extrapolated over year = £500/annum = 40 year “payback”

I’ve also had a look at what I would be paying if I was still using gas, but was keeping the house as comfortable as I now do with the heat pump over the period I have had heat meter data available.

Feb 24-Oct 24 actual: £430
Feb 24-Oct 24 if using gas: £790
9 month saving extrapolated over year = £500/annum = 40 year “payback”

I’ve been on agile since July.
Monthly bills inc VAT, export and standing charges
July £8.50
Aug £5.00
Sep £23.00
Oct £41.00

My COP is 2.4-2.8 in summer (hot water only) and 3.8-5 in heating season. Current average for the year is 4 and increasing. My COP climbs dramatically in the colder weather but obviously this comes at the cost of overall energy consumption also increasing. This is why I think a pure focus on COP is a bit short-sighted.

I have looked at my unit cost of heat. This includes all standing charges, grid charges, export income and uses monthly COP.

Feb 7.7p
Mar 8.9p
Apr 8.1p
May 10.2p
Jun 6.1p (PV installed)
Jul 1.8p
Aug 1p
Sep 3.3p
Oct 3.4p

Weighting that over the period by the amount of heat generated I get an average cost of 6.8p/kWh.

My thoughts range from

  • people don’t seem to place value on being warm (yet expect it to also be super cheap). But will spend £50k on a kitchen.
  • I think optimising for SCOP is the wrong thing…or at least solely focussing on this is misleading. I run my heat pump for 9 hours a day. It might have a slightly lower efficiency for those 9 hours, but the 15 hours of not running it definitely saves energy! Better to generate 4,000 kWh of heat when you need it at a SCOP of 4 than 6,000 kWh at a SCOP of 5.
  • I think self-learning or simpler systems really are what is needed for Joe public.
  • A focus on return on investment “penalises” already frugal users. At a fixed cost of the plant and labour cost, then the saving from reducing energy from 10,000 to 4,000 kWh is going to offer a significantly quicker payback time than going from 4,000 to 1,600 kWh. That doesn’t mean the work is any less worth doing, or that being frugal is a bad thing!
  • On a related thread, the lower the energy consumption, the greater the impact of the standing charge.
  • I got quotes for new glazing. Triple glazing surprisingly not that much more expensive double. Overall the cost would have been £7k and offered pretty limited impact on total heat loss. I didn’t get quotes for external wall insulation, I expect that would be £10-15k. Would probably make more of a difference than improving the glazing. I guess my point is you can spend a lot of money and still be burning gas. Much better to just get a heat pump.
  • Designing to the 95%ile external temperature would likely save a reasonable amount of cash for certain items like the heat pump itself, emitters and possibly also pipework. In most cases designing to 21 degrees at -4 I think is unnecessary. What about 19 at -2? OK, if gets to -4 you might have to put a blanket on but you’ll still feel pretty toasty relative to outside. Human comfort is adaptive, hence why coming into a 16 degree house when it’s 0 degrees outside feels warm, but go into the freezer aisle of a supermarkert on a summer’s day feels cold.

Ultimately for me the possible “Return on Investment” is that we might still be clinging onto a habitable planet in 50 years time.

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64

You may not have needed an R290 heat pump, but R290 has significant environmental benefits over R410a in the event of leakage anyway so it’s good the industry is moving away from R410a and R32 in my view!

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Why do you say “That doesn’t mean the work is any less worth doing”? What is it you are arguing makes the work worth doing? And if it is a saving the planet type of argument then you need to account for the embodied carbon in the more complex equipment.

As well as the standing charge, with which I agree, you should also consider the different maintenance costs of different types of equipment.

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Hi Dave, embodied carbon is a fair consideration to raise, although I think it’s pretty clear that heat pumps pay back their embodied carbon several times over in reduced operational emissions - provided low GWP refrigerants are used. Even in countries with high carbon intensity grids, operating a heat pump at a COP of 4 would bring them to parity on operational emissions.

This is a few years old now, written by a heat pump manufacturer and for commercial scale (so you know, several handfuls of salt) but demonstrates this: The meaning of life: Comparing whole life carbon for gas and electric heating - CIBSE Journal

All purchases have an embodied carbon impact, yet no one* seems to concern themselves with it for most things. The only time it gets mentioned in the domain of Joe public is in relation to technologies which are needed to allow for decarbonisation such as heat pumps, PVs and electric vehicles.

*though that is why I try to limit my new purchases, such as the hob and extra fan, so as to avoid signalling to the market to build another one. I did look at the impact of replacing my washing machine with a new one a few years ago when the bearings went and found it would never pay back on its emissions, so instead went for a second hand one. But would people forgo “life essentials” of say cooking, washing clothes, keeping food cold and keeping a house warm because of their embodied carbon impacts?

Increased complexity isn’t necessarily a proxy for increased embodied carbon (you could argue a heat pump is less complex than a boiler in some ways) - mass is a much better proxy. Although calculating embodied carbon can be pretty complex (where do you draw the system boundary…what about upstream emissions of increasing the size of the electricity grid required etc) it can be simplified to masses of a few well quantified materials, say steel, aluminium and copper for a heating system. I haven’t got the data to hand but it is something I have been meaning at looking at so I’ll try and get round to doing this for my system.

The UKGBC wrote a “roadmap to net zero” a few years ago which takes the uplift in embodied carbon into account on the trajectory to zero https://ukgbc.org/wp-content/uploads/2021/11/UKGBC-Whole-Life-Carbon-Roadmap-A-Pathway-to-Net-Zero.pdf.
I actually think the technical report they released alongside the roadmap is better as it goes into the details of the scenarios they looked at: https://ukgbc.org/wp-content/uploads/2021/11/UKGBC-Whole-Life-Carbon-Roadmap-Technical-Report.pdf. Effectively, is is a necessary price to pay.

Going back to your question - what makes something worth doing…
There are several low-lying island nations who are going to be under water in not many years time. Is it worth the global community paying £trillions (probably) to avoid that (and many other things) happening? I would argue yes. Is anyone going to ask what the Return on Investment is on not having to build whole new cities to house millions of displaced peoples (not to mention the embodied carbon of doing so)? I guess my point is that some stuff is worth doing even if it never pays back on its investment in a way that can be measured within the constraints of financial accounting.

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67

How much battery capacity does the saved radator upgrade cost pay for? (Eg an addational SEPLOS V4 Kit and x16 Envision 315Ah Grade B Bundle connected to PV inverter)

Assumung someone have a EV and hence is on Octopus IO, there is nearly a “3 to 1” saving on heatpump running costs when using battery power.

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Alan, 28mm primary is probably enough but you will need to check the max flow rate/pressure drop of a 12kW heat pump. 22mm down to 15mm for radiators (I assume that is what you’re talking about as 22mm direct to 1/2inch radiators would be unusual) seems big enough. Even 4m of 15mm pipe is a noticeable pressure drop. I changed most of my radiator valves for full bore 15mm ones on the pipes feeding the radiators, except where I needed to restrict the flow for some reason. Replacing the radiator valves is an easy upgrade.

UFH wasn’t viable for me either as I didn’t want to do another major renovation.

Diligently installed installation is always worthwhile. The builders who did my loft extension didn’t always fit the PIR insulation tightly enough - I only discovered this after they had completed the job. Very annoying.

It’s been -1C overnight and my system is working well. The performance is reduced below 4C owing to the defrost cycles on my Vaillant Arotherm. This is a consequence of the humid-but-cold weather we get in the UK. In Scandinavia, it’s very dry and cold so I don’t think you have the same rate of ice build up.

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Nothing we do in the UK can change that outcome. I expect at present the best return on investments for the environment is funding replacing all ICE scooters/moterbikes in 3rd world with electricity and PV to power the chargers. Clearly all new UK cars should be EVs and all new UK homes should use heatpumps.

So lets not pretend we are improving our heating systems to primary help other countries. Reducing LPG imports do give economic and security benefits to the UK.

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Thanks @Rachel @simon_sh @billt @gm0705 for your costing examples, I will add these to the spreadsheet and try and think through what we can make of this for how we present/discuss results on HeatpumpMonitor.org. Will update again shortly.

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Our next car will be a EV as we can easily have home charging and a car with quick heating and automatic windscreen defrost is just better. (My wife needs an automatic so the cheapest ICE are not an option.) This will practically automatically result in cheap overnight electricity and maybe push as towards a home battery.

We are thinking of getting a kitchen extension, that will then need our problem free condensing heat only gas boiler replacing. As most of the radiators are 1970s and I don’t trust the pipework to cope with a pressurised system the true cost (including grant) of having a heatpump is then little more then a new gas boiler.

UFH maybe installed for comfort/lifestyle, if all radiators replaced with UFH then heatpump will clearly cost significantly less then gas boiler to run. As due to lifestyle we like heating most of the day, with nice large radiators a heatpump will have comparable running costs to gas boiler, and stop the gas standing charge. (As I am a member of https://www.lnpg.co.uk/ I get big discounts on basic radators, so larger radiators cost me little more, but am limited with wallspace)

But without a kitchen extension or UFH, a heatpump install will include the cost of replacing all heating pipework and radiators! (New pipework does not increase properly value or quality of life.)

With my rental properties, I can’t predict how tenants will use heating and if the next tenant will understand the difference between a thermostat and an on/off switch. The combi boilers likely have many years of life left and will be an easy like-for-like replacemnt when required. I don’t trust the EPC system to reward me with a better rating for a heatpump, noone looks at the numbers just if a property is “B” or “C”. I expect it will take longer to rent a property with a heatpump as many tenants only value gas cental heating and UPVC windows.

So a heatpump would likely give a negative investment return on the rentals as primary cost is risk of property taking longer to rent. (People who like heatpump don’t wait until a property with a heatpump is on the rental macket before renting a property.)

So this concept of “return on investment” is very hard to define…

If we truely cared about CO2 emission we would move to a small town center flat that has no parking but is within a short walk of shops etc. However we don’t care that much…

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Do you @Ringi or anyone else have experience of typical replacement cycles for radiator systems and pipework ? For those that have lived in their homes for a long time , before a switch to a heat pump was the radiator system in place the original radiator system from when central heating was first installed or 2nd, 3rd generation? I guess we haven’t had wide scale adoption of central heating for that long in the UK, perhaps enough for 1 or 2 complete system lifetimes (Im assuming 30 year lifespan there)?

  • 1950-1960s central heating common in newly built homes
  • 1970s to 1980s central heating becomes the most common heating system type…
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I have once replaced a radator as it “looked old” when repainting a property. Otherwise 1970s radiator remain working provided inhibitor have always been correctly used. I will soon need to replace a very old Honeywell mechanical TRV, I hoping I can remove it without damaging the radiators.

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My radiators are 30 years old. I’ve had to replace one due to rust at the pipe connections, the others are all in great working condition, even if not perfectly white anymore. Pipes also appear to be OK. My old gas heating was losing pressure over time, the heat pump now doesn’t need topping up, so it all appears quite robust.

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My early 60s house had CH installed in 1970/71 when an extension was added. The radiators went unchanged until I installed a HP in 2023. However, they were grossly corroded and made the old system non-functional in any meaningful sense. Fixing that with new K2/K3 for the HP and a proper flush was clearly a significant contribution to the HP’s success!

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Just read your post below is my system.
Octopus install July 2024 Southern England (daikin 4Kw
Installation cost (no breakdown supplied) £8100 Bus £7500 cost to me £600.
Unit price electricity average over the hole period 7.55 p/kWh octopus int go
Heat loss from various calcs and survey 3.2 to 3.6 kW @-2
Heat recovery running 24 hours.

From MMI
Heating 226 to produce 906
DHW 162 to produce 512
Total 388 to produce 1418

Comments.
System
Daikin EDLA04EV/BLYGD, DHW Cylinder: UK.EKHWSU180JE/TK, 25 l volumiser.
11metres 28mm pipe to 3 port valve and Tank, 22 mm spine to 10mm radiator tails.

House detached circa 2014 @100 sqm
19kwh Battery system
Solar diverter
EV charger
EV.

System settings mostly gathered from this forum thank you!!
Madoka adjusted as per forum.
Hot water 48C once per day normally 3 am.
Heating set point 21C yes its warm in my house 1C setback at night.
Weather Curve upper 41C@1C lower 25C@19
In the process of balancing the system.

Observations
When external temps 4C to 7C the ASHP will run for hours drawing 250 to 400 watts with a supplied water temp 30-31C at 7 L per min DeltaT 2C. Over time (5 hours) this does tend to over heat our house up to 23C

Today external temp 1c (snow!) supplied water temp 38C at 7 L per min deltaT 5C current drawing 750 watts 2 defrost cycles observed.

Data collected via daikin MMI, Battery control system data, Myenergi system data. Octopus data.

I will be getting a open energy monitoring system just working out how to install it.

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I don’t know how old the heating system was in our 1960s house having only moved in 2021 'cept the gas boiler was 30 years old and radiators were single panel with no fins. I remember that a couple radiators were leaking and had to be turned off so two bedrooms had no heating. Another radiator would get warm during DHW cycle, which was odd.

Glad to have new radiators that don’t leak :laughing:

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Sounds like there’s a good chance that rads are still on first generation for many then? 30-50 years old and probably pushing end of life for many anyway… So perhaps the gas boiler vs heat pump comparison should include the cost of new rads in both cases for a fairer comparison? E.g the comparison shouldn’t be full heat pump system and complete new emitter system vs just the boiler swap, it should be comparison against full refit of a boiler system and new emitters…

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The difference in install cost is then something like the additional cost of the heat pump unit, say £2-3k + MCS paperwork overhead costs ~£1k?

Perhaps the following subsidy free comparison is more realistic, with the heat pump giving a 10-14 year payback.

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If the grant was at £4k it would payback immediately.

Or if it’s just a boiler swap vs a heat pump and cylinder with no radiator upgrades, running at a lower COP it might still be possible to get at the same payback range without a grant at the lower end of heat pump unit only install costs.

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I believe it’s also worth separately quantifying the cost to install a new system during the course of home renovations.

This scenario is pretty common, with new heating systems being installed when a house is extended and/or retrofitted. Often the builder/contractor will have their own plumber lined up, who will usually want to install a cheap and easy gas combi boiler system. Many end users will, under pressure from all angles, just agree to this without knowing/thinking about other options.

We were in a similar situation during the course of our renovation last year, needing an entirely new heating system, including all new plumbing. Our builder pushed us very hard to just accept his plumber installing a gas system boiler for a total cost of £6.5K.

Luckily, a friend who is an ASHP installer agreed to fit a Vaillant ASHP system instead, the total cost of which, after the BUS grant, was ~£4.5K.

Thus, in our case, the choice to install ASHP over a boiler was a no-brainer. Less cost, less carbon, more comfort. The case will be similar for most others in a similar situation, whether they know it or not.

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