Air Source Heat pump and solar to replace oil boiler

We’re 18 months into ashp on a new build. Numbers are as follows:

4 bed, 130m², 2 to 4 occupants (includes energy hungry teens), everything apart from car on electricity. Total house consumption was 6500 kWh for the first 12 months including a few weeks down to -10C in an exposed windy spot.

Always comfortably warm. Regular mostly 15mm pipework. Rads are pretty standard, just double panel with convector fins. I don’t have a measure of the exact efficiency / energy split but it still ran extracting energy at -10 and doesn’t do excessive defrosting.

Overall we’ve been very pleasantly surprised – really thought we’d struggle coming from 25 years of gas combi. The only caveat is you have to drive it properly – ie low and slow not on / off.

I do wonder if ashp theft will become a thing – it has external isolator switch and valves, so would be very easy to disconnect…..

I also know someone that bought a second hand gshp at a very good price – the original owner / install got it wrong so it extracted all the adjacent ground heat faster than it could replenish in winter.

Good job it’s not true! I’ve been following this closely and have seen nothing of the sort. There was a consultation but no decision as far as I can tell. The earliest was like 2025 in any event.

Just googled it, it’s been put back to 2026. I dotn follow it as I’ve never fitted or been interested in oil boilers.

https://www.theecoexperts.co.uk/boilers/oil-boiler-ban

Unless you’ve got lots of (good) insulation, an ASHP is likely to cost A LOT to run the heating for a house of that size, even with solar PV. The upside is that you’ve already got UFH, that seems the most efficient way to heat with an ASHP.

They’re OK on new builds (better with MVHR) with solar PV. Even then, they take a lot of balancing, need to run at a fairly constant temperature, be programmed well to ramp up/down slowly, and you’re best off with a secondary heat source if you want a quick boost as they’ll eat electricity trying to affect a big increase.

EPC’s are pretty useless if they’re produced in RdSAP – the Rd stands for reduced data and means they have even more assumptions in them than proper EPC’s that come out the back end of a full SAP calculation, as in the case of a new dwelling.

My neighbour hit granite cap and had to go to 300m. The unit they had to bring in cost more on hire than the original total install cost …..

@trailrat You’re in O&G, no? Couldn’t you have got it done at mates rates?

More helpfully – Octopus will do a survey to tell you how your house measures up in terms of insulation pipework etc and what size HP you would need. Not sure `i totally believe what they say, but it’s a place to start.

So long as your radiators are big enough there’s no reason for ASHP to ever cost more than other methods such as gas. Assuming electricity/gas price ratio stays much the same, and you get something like 3:1 return from the ASHP versus 80% efficiency (ish) from gas. What kills ASHP efficiency is having to run radiators very hot if they are under-sized for the demand (which depends on insulation of course). Gas will be able to run smaller radiators without such an efficiency loss.

Some friends locally have ASHP in an old cold stone house and are very pleased with it. Their radiators are big enough.

can anyone point me to a simple way of using the fact that I tracked oil consumption last winter to estimate how much it might cost for a similar amount of heating from an air source system??

Oil (kerosene) is just under 10kWh per litre. An old boiler is probably only going to be ~70% efficient, so your heating input will be something like 7kWh per litre of oil used.

Not an ASHP expert, but I’d expect *a similar heating input* would require, very roughly, 1/2 to 1/3 of the kWh.

As of June 2023, average costs are as follows:

kerosene (with a modern, 90% efficient boiler): 6.75 p/kWh
ASHP (2.7 CoP): 14.23 p/kWh
Mains Gas (DD rate): 11.06 p/kWh

Sauce:

Energy Cost Comparison

As someone has said it is the humidity at low temp that kills the efficiency compared to scadanvian countries

I do wonder if ashp theft will become a thing – it has external isolator switch and valves, so would be very easy to disconnect…..

For UK use to really take off, we need these in the attics. So much housing stock with little external walls to mount on (victorian terraces etc), and many of those that are will be low, damp, too easily accessed from the street, and in the way. Need more UK focused development, rather than importing set ups that work elsewhere.

Mates got a 2kw in new build. It heats the entire house. Has ufh and mvhr and a log burner for back up. 260sq mtr but. Its got 150mm insulated walls, insulation in the pad, triple glazing etc.
Still not cheap, but backed witj solar and a decent battery i can see how cheap it could be. Massive front end loading though

Just done the maths on the figures in my post above (too late to edit):

If you don’t change anything else, ASHP will be ~64% more expensive to run than your current oil boiler; a new oil boiler will be ~28% cheaper to run than your current oil boiler.

Thanks for this, exactly the kind of order of magnitude comparison I’d not managed to make yet!

After the feedback above I’ve already started ringing around to see if I can find someone willing/able to quote for a replacement, modern oil boiler, no luck yet, but there’s still time to beat the ban if it looks like the best option, particularly if future conversion to HVO looks straightforward…

You wouldn’t put an ashp in the attic because:

Noisy.

It blows out a VERY cold breeze – so you just quickly get a cold attic with restricted ingress of fresh air to extract heat from.

Even if it exhausts straight outside and only harvests air from the attic, the air in a suitably ventilated and house sealed / floor insulated attic won’t be appreciably warmer or drier than the air outside as there is such a high flowrate (so not enough time to heat the attic air from limited solar gain).

The drawing tempered air from the attic only works for positive pressure ventilation where the flowrate is tiny and you can get some limited passive daytime solar gain in autumn / spring.

the air in a suitably ventilated and house sealed / floor insulated attic won’t be appreciably warmer or drier than the air outside as there is such a high flowrate

You’re thinking new build there, I’m thinking retrofit into existing stock.

Very interesting to read all this, as we’re 9 months into a renovation/ refit of an old house in Dublin – a complete gut job, basically, of a 150-year old place. ASHP was specced, combined with underfloor/ concrete slab downstairs, radiators upstairs. We’re replacing all windows with double glazing, installing internal breathable insulation, roof insulation too. And we’ll have a wood burner in the living room downstairs.
The consensus is… mixed. ASHP zealots say it’ll be amazing, so much cheaper to run than anything else and will always keep us warm. Sceptics say we’ll be cold in winter; and nobody is able to say “look, on the one hand x but on the other y” to allow us to make an informed decision.

Ultimately, Irish regs mean we probably have to hit a certain energy rating for the finished house, and ASHP helps with that. But fingers crossed it does what we need!

You’re thinking new build there, I’m thinking retrofit into existing stock.

Yes but your still trying to put an ASHP into an attic space. That’s the issue regardless of new vs old.

Asside from the vibration/noise. You’d have to feed and vent the condenser in such a way that it believed it was outside otherwise you’ll be trying to extract heat from the cold ejected airs

Lots of FUD about ASHP about.

One of the reasons I like the protons for breakfast posts is that the poster focuses on simple things:
How much energy do you need to heat your house?
How much energy do you need to consume to provide that heat?

The rest is arithmetic.

Like EVs, I would not pick an ASHP with the intention of saving money. But I would pick one to reduce my fossil fuel burning and local pollution.

subsidies for burning fossil fuels could be with us for a while. https://www.iea.org/commentaries/the-global-energy-crisis-pushed-fossil-fuel-consumption-subsidies-to-an-all-time-high-in-2022

You’d have to feed and vent the condenser in such a way that it believed it was outside otherwise you’ll be trying to extract heat from the cold ejected airs

Well, obviously you’d need to vent to the outside. Cold air leaving through a vent rather than the CO2 leaving it from my gas boiler is fine with me. Not looking at air tight purpose built detached homes here, more the rest of us that’ll be stuck burning gas for decades to come without air source being engineered to work in existing British housing stock.

But I would pick one to reduce my fossil fuel burning and local pollution.

This.

Like EVs, I would not pick an ASHP with the intention of saving money. But I would pick one to reduce my fossil fuel burning and local pollution.

Like you, I would also do this, but £20k-£40k to install it and then having to pay more to run it, doesn’t help to sell it, does it?

The government needs to do something to help this.  They’re removed EV subsidies except for tax dodging businesses, there’s no environmental subsidies worth speaking of, but we’ll happily invest £30-60bn in Hinckley point to reduce our carbon footprint and secure energy.

It’s clear where UK government interests lie from their actions.

https://amp.theguardian.com/us-news/2019/may/13/the-planet-is-on-****-fire-bill-nye-is-getting-angry-about-climate-change

Like you, I would also do this, but £20k-£40k to install it and then having to pay more to run it, doesn’t help to sell it, does it?

TBH, it’s a gamble isn’t it. How much will your conventional CO2 emitting fuels go up in price by, how much of them will your electricity producers use to make your electricity. What will the comparative costs be next year, or in 5 years.

Thing is, if you don’t get in now, it might be too expensive to get in later. Like i should have got solar when i had the first quote 6 years ago, the increases in electricity prices would have paid for it by now (instead of the 7-9 years they quoted) that extra chunk of cash I’m now paying for my electricity means i can’t put stuff aside for solar, and round here solar installation costs have doubled as well, so i’m falling further behind.

Thankfully i have GSHP, so heating isn’t too expensive!

on the CO2 side – whilst the mix of electricity in the UK varies, more often than not if I consume more electricity (say to heat my house), isn’t that increase in electricity need most likely to be met by non-renewables? So whilst the overall mix might be 70% renewables, the marginal mix is far heavier on the fossil side (you might throw a couple more lumps of coal into a power station, you can’t make the wind blow harder), thus making the co2 argument a bit tougher?

Unless it makes the business case to build more wind turbines a bit more robust, cos coal is 4 quid a lump.

Domestic stuff can only really work if we ramp up renewables at the national level, at speed. But, as it happens, everyone I know who can afford an air source heat pump have had solar fitted at the same time. Grid only supply when dumping oil/gas is probably a big mistake, but that also means the upfront costs are even higher.

At low but above zero temperatures it can require an occasional defrost cycle to remove frost buildup. As it goes below zero it shouldn’t need to defrost as much or at all because there’s less moisture in the air to freeze

I think this is the issue for the UK as this close to zero range with high humidity (so lots of frost) is a common temperature range, better off in colder climates which may initially seem unintuitive until you consider this fact.

Larger radiators and piping is required. Not always. My CH is 30+ years old. I tried it last year by running the gas boiler at a flow temperature of 35 degrees. It was toasty as ever, and in running at the low temperature, it made my gas boiler more efficient, as it wasnt cycling as much, and condensing at all times it ran. A HP would be a straight fit in, I have standard single panel rads and 15mm pipework in a 3 bed semi. No change in either is required.

I did a similar experiment last winter.  Running my gas boiler at a 50 degree flow temp, as a heat pump would at the high end.  1928 house, solid walls, double glazing, 300mm loft insulation, and radiators that were sized for a 75 degree flow temp.  Heat loss calculations say the house needs 12kW but I think it’s more likely 10.  Heaven knows how old the pipework is.  After only changing two rads for double panel double convector, rather than singles, it was absolutely fine, and saved loads of gas.  Basically, the trick is to run the heating at a lower flow temperature for longer.  Avoids it overshooting, and means the boiler can work more efficiently.

Going to try going lower on the flow temp this year, so will probably increase the size of a couple more rads that can be done without affecting the rooms they’re in.  Not going to be putting a heat pump in in the near future (in fact about to install a new gas boiler), but wanted to know the house is capable of it and a 3 to 4kW heat pump would do the trick fine.

This has all the answers. Well 50 of them anyway. Including why you can’t put a heat pump in the loft.