Thanks Derek. That is an interesting proposal. I know zero about A2A so will go off and do some research - can you point me in the direction of anything useful? 

We don't have an immersion heater so didn't opt for solar HW diversion. In any case, we have electric showers and otherwise very low HW needs.

Posted by: @katcesca

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Thanks Derek. That is an interesting proposal. I know zero about A2A so will go off and do some research - can you point me in the direction of anything useful? 

We don't have an immersion heater so didn't opt for solar HW diversion. In any case, we have electric showers and otherwise very low HW needs.

Look on the Appliances Direct website under 'Dehumidifiers & Heating', then select 'Heat Pumps', then 'Air Sourced'. There is quite a large list of units of different sizes available. I ordered one of the smaller units from them over one year ago and installed it myself, but of course not everyone can do so.

You could contact a local AC company and see what kind of service they offer. Because A2A heat pumps don't qualify for the £5000 bribe (sorry I mean grant), they are much cheaper to install than A2W heat pumps. 😎 

Is there no way you could have an immersion heater installed on your hot water cylinder, since electric showers can be expensive to run.

Posted by: @katcesca

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Hugh F re: sticking with oil - annoyingly we can only replace the oil boiler if we relocate our oil tank because the tank doesn't comply with current regs where it is now, and relocating the tank is not a simple problem to solve! I'm going to take your optimism about it running well for a good few years yet (which actually corresponds with our heating engineer's assessment - it's a healthy beast and actually running pretty efficiently).

Long term we would prefer to heat using renewables not oil but we can't do that if the tech/costs aren't there yet. 

The bunding regs only apply when you are a certain distance to a watercourse, many oil supply companies get that wrong and tell you that all tanks need to be bunded. Do check that they are not incorrect in their understanding of the regulations

@HughF the issue is that our oil tank is inside part of the building (in a large garage) and it should be outside, X distance away from structures etc. The tank is insufficiently fire protected for current regs. We don't own the land in front of the building so would have to adjust titles etc to site it outside. Not an easy fix! 

@katcesca ah, yes that's a complication....

@katcesca - ah the joys and pains of replacing oil tanks. I had a working boiler, and a 25+ year old tank with very early minor pin holing, not even really that, but it needed replacement. Fast forward four years and I now have an ASHP. Not only did I have to grapple with oil tank regs, I also have a listed building, and that caused all sorts of fun and games, including the dreaded virtual bats in belfry (in the end I managed to persuade the council their bat modeller was a bit batty, needed to get out more often, and look for real bats).

I had and have a similar situation to yours - old leaky building, high thermal mass, previously heated successfully and reasonably affordably by oil (much smaller, but pro rata I think things will be much the same). The ASHP quotes I had, and the proposed 'savings', were all over the place (more comedy modelling going on, what if spreadsheets where the installer dials in the numbers to make their quote look good) but you actually have some real data that doesn't need to be modelled at all, your past annual oil consumption. You can use that, as you did in your original post to determine the energy needed in kWh to heat your house to the level you have it heated to. The projected demand and costs from the installers are just models, not real life. That said, there are some rather curious observations I have about my past oil use in litres (and so kWh consumed) vis a vis what my ASHP consumes and produces, with the latter being around 3 times what it consumes (ie a COP of three). I have yet to resolve these conundrums but consider this: using oil, I used say 1200L per annum, so 12,000 kWh per annum of delivered heat, perhaps a bit less after factoring old boiler inefficiencies. I suspect (I don't know, see below) I will use (consume) about 8500 kWh of electricity for the heat pump over this heating season, which at a COP of 3 means it is delivering well over double (25,500kWh) the heat energy delivered by the oil system (12,000kWh, probably less). But the house is roughly at about the same heat (comfort) level as it was under oil. Something doesn't make sense here...    

Conundrums aside, I have yet to have a whole heating season using only a heat pump for heating and DHW, as the heat pump only went in last February, and for the rest of that heating season usage was rather all over the place, for a variety of reasons, so not very informative. Over this heating season, it looks as though:

(a) in mild to moderate weather, looking at weekly consumption, the heat pump uses slightly less that I used in the past three years, when I was using standard mains Argos heaters to only heat a room or three, but uses a lot more in cold weather. Overall, I suspect they may cancel out, and the full seasons use will be similar.

(b) I really need to wait for the end of the heating season to make a comparison with further back, when I was using oil, because I only have annual usage data for oil. I suspect, as others more knowledgeable have suggested, that it will turn out that oil is currently the cheapest (in £££) fuel, but it gets a bit more complicated than that because there is also the kWh usage and production with due attention to efficiencies to take into account to make sure we are comparing like with like, or if not make due allowances.

I write up an actual costs (in kWh, and only then in £££) comparison here on the forum once we get to the end of this heating season.       

@cathoderay your oil boiler was probably closer to 85% efficient* so that 1200ltrs of oil delivered 10,200kWh of useful heat into property.

Your electricity consumption seems high, or you are indeed heating the property more.

*source, Worcester Danesmore non-condensing oil boiler spec sheet

Posted by: @hughf

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your oil boiler was probably closer to 85% efficient

I think it was probably less than that, it was a 25 year old Grant triple pass Euroflame boiler. Net result is still the same, though, the ASHP appears to put around twice as many (or even more) kWhs into the building compared to the oil boiler to achieve comparable warmth/comfort levels. It doesn't make sense, hence the conundrum.

The electricity use for Argos type convector/fan heaters vs heat pump figures make more sense. Both are around 9000 kWhs per heating season (high because it's an old leaky building). Typically during the Argos period I had one or two convector/fan heaters on, heating only one or two rooms, lets say on average 2-3 kWhs per hour, which is very roughly what the heat pump uses. But as it is a heat pump that means, at a COP of 3, it is putting out 6-9kWhs per hour, which is a reasonably sane estimate of what my house needs in normal outdoor temp conditions (estimated heat loss at design temps of 18-21 rooms at -2 outside is 12.4kW). Basically, I can use roughly the same amount of energy now, with the heat pump, as I did when I used the Argos type heaters, but instead of just heating a room or two, with the rest of the house perishingly cold, I can now heat the whole house, because I have an output of lets say four 2kW Argos type heaters on all the time, two upstairs and two downstairs, if that makes sense.

It's a rather different story when it is colder outside, around zero, the energy use skyrockets (double whammy of more energy needed per se plus less efficient production of that energy), and furthermore the house ends up a few degrees below where it should, a result of the heat pump being under-spec in these conditions (because Headroom Heat Pumps' heat pumps don't in fact have the headroom they claim they do). But that's another story, that has been told many times before in various places on the forum.

Moral of that tale for prospective heat pump owners is triple check your proposed heat pump's output at low outdoor temps. It is very possible that a heat pump that has a headline output of xx kW in ideal (warm) conditions (when you don't need xx kW) will only put out around 80% of that figure in cold conditions, eg my Midea nominal 14kW (loads'a'headroom) only puts out around 11.4kW at around zero outside (zero headroom, in fact its negative headroom as it it's less than the demand, 12.4kW). 

We have a 1920's house with a new big extension. We externally insulated and rendered the existing house with 70mm celotex along with high quality modern double glazing.  My last house we used internal insulated plasterboard with 45mm celotex and that worked out at maybe half the cost of external insulation with no need for render.

Radiators with an oil boiler are sized for T+50 (ie 65-70 degree water) .... with ASHP you aim for T+30 (50 degree water) ... that means much larger rads. My wife didnt want the standard ECO rads and we ended up with oversized 4 column rads

https://www.justradiators.co.uk/lux-heat-oxford-4-column-horizontal

And actually even at 30 degree heat they warm the rooms (though when sub zero outside that is not enough hence the use of weather compensation on the ASHP).

We have only had the ASHP installed for couple of months and its clear getting the setup optimal is not straight forward ... I think we are almost there and my spreadsheet **guestimates** our annual electric heating cost will be around 8400kwh almost £3000 at 0.35p/kwh

I think thats similar to what we spent on oil given the current oil price at boiler juice. That said before at night thermostat was set to 16 degrees and now its just constant 19 in whole house. I think once we buy curtains that will make a big difference as overnight the extension UFH struggles to heat the extension especially when sub zero, note we have ceiling apex over 4m and there is alot of glass in each wall.

My friends asked if I would recommend ASHP, early days for me, but I think if you have gas, its cheaper so being green is the real driver there, if you have oil, it can be work but the journey has not been pleasant for us .... costly and disruptive having all new pipework in house as well as the stress of getting daily heating use down from crazy peaks of 80kw with average of 40kwh to more acceptable average of 30kw ..... though as I stress we have only been using for couple of months .... so others on this forum best for real world annual costs.

Posted by: @katcesca

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Derek, re the gold plated rads (!) in the quote the actual radiators aren't the bulk of the cost, they are itemised at about £290 each for large Stelrad K2s which is about what I can find them for on eg Plumbnation, but the pipework and fittings add thousands on to the overall quote. Because some of our radiators are outdated and undersized anyway, I'm looking at one option being to start upsizing them piecemeal now, as and when we can afford, with TRVs fitted. 

TLDR: I nearly fell off my chair when I saw your cost for radiators and fittings.

That said, it matches with the ballpark that a number of "ASHP companies" (whom I told not to come back) waved at me when I think they were trying to take me for all they could back in 2020 under RHI. This is a significant part of your cost you can really easily work down.

Make sure you're speccing "normal" radiators rather than "style" ones. You can pay double or triple for colour, flat-front finishes (which also reduces the output) or similiar.  unless you really want to spend the money on looks - in which its your money! Just use screwfix pricing its as good as any. I just had a quick look, I had to go into the "flat finish" models to be able to spend 290 on a stelrad at screwfix. Their "standard finish" equivalent sizes being around half that price.

If you're looking at one enormously wide one consider two half the size (if it makes sense for the room). it might well be less than half the cost. e.g screwfix Flomasta K2 600x2000 = £340. Flomasta K2 600x1000 £69 !! The non-linear step seems to be once you go over 1200 wide.

radiators are very do-able yourself - not beginner change-a-light-bulb DIY, but not grand-designs-build-your-own-house level either.  If done in summer, you can take your time with the system drained. I did the ones that needed doing in my whole house this summer for less than £1k. That was 6 k2 rads (between 1000 and 1400 wide) plus fittings. If it needs re-piping as well its more about time rather than materials as you've got to lift/cut floor boards for access etc - but even so its not thousands more.

If you're not confident or don't want to take it on as DIY - fair enough - you can get any local plumber to do it . They do NOT need to be ASHP expert to fit rads. You just need to spec the rads so they are ASHP-level in output. Their labour rate will be way less than what the ASHP specialists will be factoring in, and you can shop around with whoever's local . You can look at the "less experienced" end of the local market -  you may be able to get someone cheaper who's recently out of training college / apprenticeship rather than a 30 year veteran.

Posted by: @katcesca

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@Marvinator80 we fitted 4Kw solar array and 10.5kw battery in August - just under £10k all in. We did this phase first to see what real-world impact it had on our electricity profile. Initially we were optimistic we could make something like your plan work, but it doesn't pan out like that actually. Broadly, for us an ASHP would use around 13000kwh/yr and the solar panels will generate maybe 3000. 

Annoyingly our roof is very steep and the angles mean that we don't get amazing solar gains from it, but nonetheless the system is on track currently to reduce our electricity usage by at least 50-60% (was 5000kwh annually). We have just started charging the battery at night on Octopus Agile tariff to take advantage of cheap rates and so are using zero grid electricity in daytime hours - early signs are encouraging about how much this will knock off the remaining bills but obviously the energy price volatility make that saving hard to calculate long term. There aren't any other cheap tariffs currently that work with a battery if you don't have an EV. 

However, having it up and running, I don't really think the solar/battery would make a huge dent in ASHP running costs for us - in cold weather a 14Kw heat pump is going to be using far more a day than the 10kw we can download cheaply onto the battery overnight, and on a December day our panels will generate between 0 and maybe 3/4Kwh. And we need heating in the daytime, not at night. 

Yes, we'll be generating a lot of energy in the summer months, but we don't need to heat our house in summer anyway. The solar panels do cover our electric showers, so we have very low hot water demand from the oil system. 

If I could access a £9k grant for the ASHP the sums would stack up differently, but I can't!

@katcesca you've missed something. you do not need to have an EV to access TOU tariffs like octopus Go (12p/unit 4hr offpeak) - despite what some of the marketing may lead you to. as you are on agile already you can look into it. You do need one for Intelligent octopus (10p/unit 6hr offpeak) though , that specifically requires access to manage the charging of the EV (long story, other forums).

anyway, get this working and you can fully charge your battery overnight in winter cheaply.  If you've got the capital to buy the batteries (and suitably large electrical connectivity, and somewhere to put them) then adding more batteries WILL make a dint in ASHP running costs. I've not actually put the ASHP in yet, but with 40kWH of battery, charged overnight on octopus at 10p/unit, and an assumed COP of 3, I'll be able to generate 120kwH of heat for £4. how much the house needs is a separate question on the other side of the equation , but my worst case days (210m2 house) are 130kWh of gas.

solar at 4kw does seem a little small but I guess that depends on your roof. See if you can find anyway to make it bigger! any land space that will take a ground array?

your DHW load estimate numbers seem high to me - how many people in the house? you can also look at running your DHW entirely on electric for a while. Turn off the oil heat of the cylinder. Run the cylinder immersion overnight on octopus cheap electricity, through a metering device. This will tell you exactly how much DHW energy you use. also the solar will help a lot with this in summer - get a diverter. If you buy an Eddi, it will do both jobs  - the APP (or API) will tell you how much usage per day from solar, how much from grid overnight boost, and do the diversion which is of course is main job. I did this for the whole of 2022 and I now know exactly what my DHW load is - less than the estimates.