Posted by: @abernyte

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Posted by: @mjr

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which should be about 5,500kWh of electricity with a decent ASHP,

Okay, with a ASHP with a SCOP of 2.5 that still leaves a bill of around £2600. Heat with an oil boiler and that is sub £1,800 with around 6000kWh for heating.

My point is the danger in such a built in disadvantage to change will prevent uptake of clean renewable heating. Look at this and other similar fora and see the number of dissatisfied ASHP users where it turns out that the Heat pump is actually performing as expected but it is the concomitant bill attached to using it that causes the problem.

Probably better working with real figures where possible rather than approximate calculations on theoretical consumption and averaged prices.

We got our ASHP installed mid December 2021, and would have been due another delivery of oil at that point (it was around 67ppl at that time). We would have needed another oil delivery around May at which point it had jumped hugely in price to approximately 105ppl. Our heating and hot water bill, therefore, would have been (based on our normal consumption prior to the ASHP) about £1,800. In the same time we've been charged just under £1,900 for electricity by Octopus (around 22p/kWh peak, rose to 34p and is now 43p), so we're about even.

HOWEVER.....

Over the year, pretty much bang on 45% of our usage was nothing to do with the ASHP, so we would have had to spend that on electricity anyway. As a result, the cost due to heating and hot water (i.e. what we used the oil for) was around £1,100. I have to adjust that upwards to take into account the energy from our solar PV that would otherwise have incurred a cost and that gives us a yearly heating and hot water cost of about £1,250. As a result, we're better off with the ASHP by about £550, and that's ignoring the extra £500 we were paid by Octopus for exported solar PV energy.

Bottom line is that the ASHP has saved us about £550 in heating and hot water energy vs our old oil system, and the solar PV has benefited us in free consumption and paid export to the tune of about £1,000.

Posted by: @mjr

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Look, if you hate heat pumps, just say so.

Whoa...I am delighted with my ASHP. It performs outstandingly and has slashed my fuel bills from my previous LPG +solid fuel. No where am I denigrating ASHPs. I can routinely get a COP of 4+ in a large property but I know that is not the norm for many of the installations on here.

I am posing the question as to at what point this technology is no longer affordable when fossil fuel heating is so much relatively cheaper.  It is a fair question to ask when ASHPs are getting installing into houses occupied by those on fixed low incomes.

Posted by: @mjr

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how many oil boilers aren't connected to mains electricity which therefore requires payment of the standing charge?

Fair point, but it currently means ASHPs and oil are neck and neck per kWh. I may or may not have been a bit generous with the COP I used, and a bit harsh on oil boiler efficiency. If those were adjusted, COP down a bit and boiler up a bit, oil would come out cheaper again. But I suppose the real point is that, under current pricing, and without 'extras' like solar, they have similar running costs, the bigger difference is the installation cost. Given a median installation cost of around £12,500 for and ASHP, even with boiler upgrade scheme that means a median householder outlay of £7,500, maybe twice what an oil boiler would cost. That of course assumes a new boiler is needed, many will have perfectly capable oil boilers in place, costs having been lost in the past. 

Posted by: @mjr

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If someone is going to take on a listed building and do nothing to improve its energy efficiency, they'll need deep pockets no matter what the heating.

I am continuing to do what I can (currently adding secondary glazing) but most of the heat goes out though the solid stone walls. But I've always accepted an old leaky building will cost more to heat, whatever the fuel, it's part of the price I have to pay to live in an attractive old building, in much the same way that living in the country means higher travel costs than if I lived in a city (more miles, not less mpg). Likewise, in the past, being off the gas grid meant we couldn't avail ourselves of cheap gas heating, this is just they way it was.

Come the end of this heating season (my first whole season with an ASHP), I will add up total kWh usage compare it to past oil use, and post the figures here. So far (but a bit premature to say), it looks like they will be similar, but there is a mystery, alluded to in other posts, if oil and ASHPs use about the same amount of energy in, then the energy out in the latter is around three times as much, yet the 'comfort level' is pretty much the same. It doesn't make sense.      

Posted by: @abernyte

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is going to mean an annual bill of around £5,500 on the worst case scenario of 048p/kWh with oil costing £3,500. That gap is not sustainable. 

Ultimately this will come down to the efficiency you can get out of the heat pump.  Assuming a SCOP for a heat pump installed properly being round 3.7 then we have a bit of headroom over oil right now.

There should be properties be able to average higher than 3.7.  I think there will be properties where installing a heat pump is an altruistic action on behalf of your grand children.

Posted by: @cathoderay

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Fair point, but it currently means ASHPs and oil are neck and neck per kWh.

Depends on the CoP, for me, based on my tariff[s] I need to get above 3.4 right now to be cheaper than oil.  Hence the need to get the installs done properly.

Posted by: @abernyte

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No where am I denigrating ASHPs.

I suggest that assuming a SCOP of 2.5 for a non-faulty installation is denigrating ASHPs.

Posted by: @abernyte

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Posted by: @editor

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I've just done the maths this weekend – based on our consumption with oil at 75p/litre (that's our oil club price this weekend) and electricity at 34p/kWh if temperatures are above 5C our ASHP is about 20% cheaper to run than oil. As temperatures go up (over 5C in our case) ASHPs will continue to be cheaper to run.

That is surprising and welcome. Oil at 75p/litre seems very keen, Boiler Juice are quoting 84p/litre today. How many litres of oil v how many kWhs of 'leccy was that nominal calculation using (without prying to deeply into your domestic energy consumption!).  I understood that 1 litre of kerosene gives 10.3 kWh of energy so the ASHP COP will have to be 3.3 to break even at 0.34p/kWh for 'leccy, or have I missed something?

If we ran oil only, we'd get through about 800 litres in a month or about 1,200kWh of electricity – that's with ambient temperatures above 4-5C for ASHP. If it dropped below that for weeks at a time, the boiler becomes cheaper. That's why the bivalent approach is helpful for us. When it gets cold, the HVO boiler does the heavy lifting and when it's warmer the ASHP takes over with better efficiencies. 

The break-even COP for me, with my current gas boiler (which is hopefully getting retired this summer), and prices at 34/10.9 is 2.9.

My gas boiler is only 72% efficient according to the data plate.

I swapped my gas boiler for an ASHP and it is far, far cheaper than it would have been on gas. A combination of 3 things: 1) old gas boiler being very inefficient, (2) investing in solar panels and battery storage (with a cheap overnight rate for charging), and (3) gas prices actually being quite high now compared with elec, so the ratio of elec:gas prices is only 3 (vs nearly 6 when I first did these calcs before installing). Tbh any one of those things would have brought it to approximate parity with gas, but all 3 of them makes it kind of a no brainer.

Posted by: @editor

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If we ran oil only, we'd get through about 800 litres in a month or about 1,200kWh of electricity –

Thank you Mars that is helpful but I am still confused. 800 litres of kerosene should give 8240 kWhs of energy. If your equivalent is 1200kWh of electricity then the HP must be running a COP of 6.8 

Posted by: @editor

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If we ran oil only, we'd get through about 800 litres in a month or about 1,200kWh of electricity

Mars - that's a huge amount of oil - I used not that much more (between 1000 and 1200 litres over a whole heating season to heat my old leaky building. In the old oil fired days, I never felt the house was cold, so it is not as if I was skimping. At 10.35 kWh per litre, that is 82,800 kWh per month (@abernyte - you dropped a zero) - a huge figure. If the 'about 1,200kWh of electricity' is the heat pump input figure for a month (I think that's what you're saying), then at a COP of 3.5 that is 4,200 kWh, about half what you would get from oil.

The numbers don't make sense! 800 litres of oil is not 'about 1,200kWh of electricity'.

But nor do my figures make sense, only they go the opposite way. Lets say, per heating season, rather than month:

Oil heating: 1100 litres per season and 80% boiler efficiency = 1100 x 10.35 x 0.8 = 9,108 kWh net heats the house OK

ASHP heating: looks like it will be about 8500 - 9000 kWh energy in per season, at a COP of 3.5 that's 30,625 kWh kWh net to heat the house

Is oil somehow a magic juice that produces kWhs that are three times more effective than tawdry old ASHP kWhs?

Either I am being very thick, or something is seriously wrong with the numbers.   

Posted by: @scrchngwsl

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investing in solar panels and battery storage

We need to compare like with like, if ASHPs have little helpers in the background, of course they will appear cheaper, even when they might not be. That doesn't mean your total setup isn't a no brainer, it's just having the other stuff makes it less straightforward to tease out how the heat pump is doing.

Posted by: @cathoderay

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Posted by: @editor

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If we ran oil only, we'd get through about 800 litres in a month or about 1,200kWh of electricity

Mars - that's a huge amount of oil - I used not that much more (between 1000 and 1200 litres over a whole heating season to heat my old leaky building. In the old oil fired days, I never felt the house was cold, so it is not as if I was skimping. At 10.35 kWh per litre, that is 82,800 kWh per month (@abernyte - you dropped a zero) - a huge figure. If the 'about 1,200kWh of electricity' is the heat pump input figure for a month (I think that's what you're saying), then at a COP of 3.5 that is 4,200 kWh, about half what you would get from oil.

The numbers don't make sense! 800 litres of oil is not 'about 1,200kWh of electricity'.

But nor do my figures make sense, only they go the opposite way. Lets say, per heating season, rather than month:

Oil heating: 1100 litres per season and 80% boiler efficiency = 1100 x 10.35 x 0.8 = 9,108 kWh net heats the house OK

ASHP heating: looks like it will be about 8500 - 9000 kWh energy in per season, at a COP of 3.5 that's 30,625 kWh kWh net to heat the house

Is oil somehow a magic juice that produces kWhs that are three times more effective than tawdry old ASHP kWhs?

Either I am being very thick, or something is seriously wrong with the numbers.   

Posted by: @scrchngwsl

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investing in solar panels and battery storage

We need to compare like with like, if ASHPs have little helpers in the background, of course they will appear cheaper, even when they might not be. That doesn't mean your total setup isn't a no brainer, it's just having the other stuff makes it less straightforward to tease out how the heat pump is doing.

 

@cathoderay,

Are you sure you're getting a SCOP of 3.5?  If you're running flat out when it's cold and have a flow temp of c.50 (iirc) I doubt it's that high. It might not account for all of the difference but maybe some. 3.5 is at the upper end of what I'd expect.