Switching from oil to a heat pump

[Avocet]

I'm looking for experiences of switching to a heat pump, please? Octopus are offering a good deal with the government grant right now. 1995 detached house, 220 square metres. Windy spot in Cumbria. Currently has a Worcester Heatslave 20/25 oil boiler which was put in when the house was built, so it's had a good innings, but spares are getting hard to find and of course, oil prices are eyewatering right now. No mains gas to the area so everything else is electric. If the temperature drops much below zero and it's windy, the boiler can only just about cope, working flat-out.

Octopus reckon a 15,5 kW air source heat pump will be up to the job. Before I take the plunge, does anyone have any experience of this sort of change on a similar property please? Any pitfalls I need to look out for, or questions I should ask? We have a 100 Amp house fuse but with everything being electric (and having an EV), they're suggesting I go to the DNO and ask for the house fuse to be doubled to 200 Amps. Will the cable to the house need to be upgraded?

 

[Rodders53]

AIUI your DNO will likely want to install a 3 phase supply... not uprate to 200 A single phase... but ask them what it will involve and how much it'll cost. (Do be seated when reading the response). Then you'll have house on 1, EV on another and HP on third??

A 15.5 kW output heat pump at a very lousy COP of 1 is 15.5 kW so circa 67 Amps (a tad more inrush, possibly). However we'd expect a far better COP, even in the depths of winter... Likely under 30 Amps in a worst case situation and normally a lot less.
The obvious 15.5 kW unit is the Grant Aerona 290 (Propane refrigerant) https://www.grantuk.com/professional/products/air-source-heat-pumps/r290/ with a rated max of under 30 Amps... and a SCOP of 3.33... Also can heat the CH to 55C which is not that dissimilar to an oil burner.

Mind even with oil at 10p/kWh (circa £1 a litre) it'll be hard to make the numbers work (in payback terms) if leccy is near to 30p/kWh - even if one adds battery storage and cheap overnight tariffs in?

NB allow 32 A HP, 32 A EV leaves 36 A for the house load (washer, cooker etc.,.) and any modern smart EVSE will throttle the charge rate back to protect the total incoming below the set house limit at any times that is needed.

Get alternative quotes (e.g. from a Heat Geek installer locally) that will do a proper survey and heat loss calculations to determine what will be needed.

Check out the MSE Forums' Energy/Heat Pump sub forum where there are very knowledgeable types on, as well as here.

Octopus have a rep for cherry picking the simpler installs...

 

[Avocet]

Thanks, that's all really useful! And yes, the Grant Aerona 290 is indeed the one they were proposing.

I'll have to do my sums carefully. We spend about £2k a year on heating oil (and that was before trump started playing the fool in the Middle East! If it stays as it is, we'll be nearer £2.7k a year. Octopus have a "cosy" tariff that's 13p / kWh for 8 hours a day, broken into three - (2 x 3 hour and 1 x 2 hour period). Really not sure how that's going to work with the EV as well. 36-40p at all other times and of course, 40p when you're going to need it most, in the early evening! As the wife is retired and I work from home most of the time, we're heating it all day, so it's not going to be a simple calculation.

 

[Rodders53]

Octopus have a "cosy" tariff that's 13p / kWh for 8 hours a day, broken into three - (2 x 3 hour and 1 x 2 hour period). Really not sure how that's going to work with the EV as well. 36-40p at all other times and of course, 40p when you're going to need it most, in the early evening! As the wife is retired and I work from home most of the time, we're heating it all day, so it's not going to be a simple calculation.

If you are with Octopus and have a smart meter you can download your 1/2 hourly usage for the base load / cooking / EV... and then use some 'averages' monthly/quarterly...

You need to work in kWh numbers rather than £s... £2.7k of kerosene would get 2,700 litres at £1 a litre or 27,000 kWh (roughly). At 80p you'd get more (33,750 kWh) ... and the rate is volatile with Trump's antics.

Octopus HP only Cozy: The 'killer' is their swingeing peak rate from 1600-2200 every day!! {For my Postcode a fix is 31.32p day / 15.36p cozy / 46.98p peak! variable is 26.67 / 13.09 / 40.01 - number will vary with Region.}

Octopus have a plethora of Time of Use tariffs... so worth looking at others (and other suppliers' tariffs in the longer term). If I put in that I have a compatible EV/charger and a HP Octopus suggest that Intelligent Octopus Go at 8p/kWh for 6 hours at night 23:30-05:30 and 34.32p/kWh day is the most likely one (only fixed rate is offered).

But you can use your own known kWh numbers for heating / hot water and allocate them to times of day to work out if a TOU tariff even works for you... Based on best guesses and advice from reputable installers.

Bear in mind that the 'rule of thumb' is to run 24/7 at two temperatures 'comfort' and 'set back' a few degrees lower, so the building fabric never cools right down. (Set back temp may never call for heat in some rooms). This means the HP never has to work flat out to reheat a cold building, and risk a poorer COP. (An MSE forum member matelodave lives in the fens with a similar wind chill issue you describe. I'd recommend you read some of his postings there).

I moved to Octopus in March anticipating going onto their Intelligent Octopus Go (IOG) EV tariff... and got a fix at 22.09p/kWh while the smart meter was accessible to them... It'd be more expensive to move to IOG than charge at the fixed rate pricing by my calculations.

I have an oil burner and a Heat Pump might make sense if/when my Grant boiler fails... but I'm still burning last year's 53p/litre delivery. We're 1000-1100 litres per annum (but use air to air heating in the shoulder months). Our electric use is much higher in Summer due to those A-A units cooling. I know I'll have to order kerosene in the not too distant future, so am keeping an eye on the price.

DO please get other Quotes and equipment recommendations from reputable local installers https://www.heatgeek.com/heat-pump-installers-liverpool-the-north-west

 

[Avocet]

If you are with Octopus and have a smart meter you can download your 1/2 hourly usage for the base load / cooking / EV... and then use some 'averages' monthly/quarterly...

You need to work in kWh numbers rather than £s... £2.7k of kerosene would get 2,700 litres at £1 a litre or 27,000 kWh (roughly). At 80p you'd get more (33,750 kWh) ... and the rate is volatile with Trump's antics.

Octopus HP only Cozy: The 'killer' is their swingeing peak rate from 1600-2200 every day!! {For my Postcode a fix is 31.32p day / 15.36p cozy / 46.98p peak! variable is 26.67 / 13.09 / 40.01 - number will vary with Region.}

Octopus have a plethora of Time of Use tariffs... so worth looking at others (and other suppliers' tariffs in the longer term). If I put in that I have a compatible EV/charger and a HP Octopus suggest that Intelligent Octopus Go at 8p/kWh for 6 hours at night 23:30-05:30 and 34.32p/kWh day is the most likely one (only fixed rate is offered).

But you can use your own known kWh numbers for heating / hot water and allocate them to times of day to work out if a TOU tariff even works for you... Based on best guesses and advice from reputable installers.

Bear in mind that the 'rule of thumb' is to run 24/7 at two temperatures 'comfort' and 'set back' a few degrees lower, so the building fabric never cools right down. (Set back temp may never call for heat in some rooms). This means the HP never has to work flat out to reheat a cold building, and risk a poorer COP. (An MSE forum member matelodave lives in the fens with a similar wind chill issue you describe. I'd recommend you read some of his postings there).

I moved to Octopus in March anticipating going onto their Intelligent Octopus Go (IOG) EV tariff... and got a fix at 22.09p/kWh while the smart meter was accessible to them... It'd be more expensive to move to IOG than charge at the fixed rate pricing by my calculations.

I have an oil burner and a Heat Pump might make sense if/when my Grant boiler fails... but I'm still burning last year's 53p/litre delivery. We're 1000-1100 litres per annum (but use air to air heating in the shoulder months). Our electric use is much higher in Summer due to those A-A units cooling. I know I'll have to order kerosene in the not too distant future, so am keeping an eye on the price.

DO please get other Quotes and equipment recommendations from reputable local installers https://www.heatgeek.com/heat-pump-installers-liverpool-the-north-west

Again, many thanks. I did ask about keeping the oil boiler as backup, but to get the government grant (which is pretty generous right now!) they said they have to take the old oil boiler out completely. Obviously though, in a rural area, there's no problem with me burning wood as a backup.

I'll sit down and the the sums. I do have the half-hour data. The problem is that we're on the "Go" tariff at present for the EV, but that's changing to a random 6 hours of cheap electricity in each 24 hour period. It might not even be 6 continuous hours, so it's going to be very difficult to plan (if we stay on the Go tariff). I'm starting to wonder if we're going to end up with a house battery too!

Another slight worry is that we've had the odd power outage in the past, usually trees taking down power lines. Right now, I have a generator and it's really nice to be able to run the oil boiler off the generator when the electricity fails. I'll miss that! Fortunately, it's only between 3 and 24 hours without power, every other year, on average.

 

[ericmark]

We spend about £2k a year on heating oil (and that was before trump started playing the fool in the Middle East!

I was paying around £800 a year before Trump, so it does seem something wrong. I asked one question when it was suggested to me to have a heat pump, with an electrical failure how long will the central heating continue to run. With oil, it would depend on how much in the battery when it failed, but could very well run for weeks. With solar recharging the battery. With a heat pump, a battery and solar panel large enough to run it for even a day, would cost an arm and a leg.

 

[Avocet]

I was paying around £800 a year before Trump, so it does seem something wrong. I asked one question when it was suggested to me to have a heat pump, with an electrical failure how long will the central heating continue to run. With oil, it would depend on how much in the battery when it failed, but could very well run for weeks. With solar recharging the battery. With a heat pump, a battery and solar panel large enough to run it for even a day, would cost an arm and a leg.

Yeah, that is a bit of a worry! And if I had a generator big enough to power a 15.5 kW heat pump, I'd probably just be able to heat the house with the generator! However, for the number of times it happens, I might just light the open fire and make a hot water bottle.

 

[ericmark]

There is no reason why a heat pump should not be driven by an oil engine. There are with refrigerated transport often duel fuel electric and oil engine.

However, to get top efficiency with a heat pump, the motor speed is adjusted rather than being turned on/off. When I played in 1980, only control was on/off.

And inverter motor control means less in rush, so the idea of diesel-electric, or TVO-electric is on the cards. But as to cost, not so sure.

Once bitten twice shy, I had a vented tumble drier, with an option of 1 or 2 kW for the heating, at 1 kW drying took longer but not twice as long, around 90 minutes, replaced with heat pump drier at 650 watt for 2.5 hours, so the sums vented 1.5 kWh heat pump 1.625 kWh. OK not quite like for like, one the vented was a bit smaller, two the vented was causing mould on the walls due to window left open, three vented was not humidity controls and sometimes needed to be put back on, and four, the heat pump took longer, no option to compare a 650 watt vented to a 650 watt heat pump.

But basic fact the heat pump was in real terms no better to a vented tumble drier, in spite of all the hype. I am pleased with the heat pump tumble drier as I can close the window so better security, and it is more automated, but it is not as cut and dried as people try to make out.

So more to the point, why do I use less oil to you? Whole host of possible reasons.
1) I use thermostatic control in every room, my electronic TRV heads ensure a room is only heated when and by how much required, no heating of living room in dead of night, or bedroom at midday.
2) In the summer my domestic hot water (DHW) is heated with an immersion heater from the excess solar. Not oil.
3) I have the boiler serviced, although that reminds me, he has not turned up this year.
4) New double glazing all around the house.
5) Reasonable loft insulation.
6) Not sure about cavity wall insulation.
So house is on three levels, 5 bedrooms, but 2 used as a craft room and office. Dinning room hardly ever used, more of a store room, only use the front kitchen, the back kitchen only used in summer with a BBQ, also lower bathroom hardly ever used, mainly use mid-floor shower room/toilet. And lower living room only used when we have a BBQ.

So of the 14 rooms, one the utility room not heated, so 14 heated areas when I include the hall and landing, only the rooms used are heated. As and when required. The boiler is 20 kW and is really too big, I can turn the lower floor completely off with a motorised valve, the middle and upper floors have 10 electronic TRV heads, and two wall thermostats, and one of the TRV heads and the two wall thermostats can turn on the boiler.

The oil tank I assume 600 gallon, will not quite last the year, well it may do, but at ¼ full I get a top-up, I don't risk it running out.

Electric wise I pay around £200 a year, including standing charge, I have a 6 kW solar array and a 5 kW inverter and 6.4 kWh of battery, and us an off-peak tariff, so summer exporting at 12p/kWh and importing at 8.625p/kWh, but winter the battery will run out, so then paying 32.277p/kWh, and standing charge 32.277p per day.

December down to 125 kWh for the month from solar, but July it was 976.4 kWh in 2024 it was 5139.1 kWh and 2025 it was 6028.5 kWh, so a large hunk of my energy needs is from solar. To use a heat pump to cool the house great, as if it needs cooling then loads of solar, but to heat the house, likely no solar to run the heat pump in winter.

 

[Rodders53]

Do your research / due diligence on other forums: MSE has good stuff, perhaps SpeakEV where some EV users gamed battery / solar and cheap off peak slots (that made Octopus change their pricing of smart charging hours), and there will be others.

AIUI Only Intelligent Octopus Go (IOG) has the potential for daytime 30 minute slots for EV charging (none are guaranteed), plus the 6 hours whole house and 23:50 to 05:30... (but EV's can only charge for a total of 6 hours at the cheap rate in a noon to noon 'day').
IOG requires compatible EV (my Volvo isn't) and/or a compatible EVSE ("charger") my Hypervolt Pro 3 is.

Octopus Go is for non-compatible EV/EVSEs ... https://octopus.energy/smart/go/ and is at a fixed 00:50 to 05:30 so only 5 hours (whole house and EV).

Remember a 15kW OUTPUT heat pump will 'only' consume around 5kW (that Grant says 6.9 kW 30 A at full whack)... and probably less. Plus a home isn't gonna drop in temperature unduly in a few hours... and you have a wood burner (more than I have).

Reading suggests Tesla battery-inverters can safely 'island' a home during power cuts... Much more difficult to do with a generator in the mix (but anything is possible). All more expense of course.

 

[drives]

Thanks, that's all really useful! And yes, the Grant Aerona 290 is indeed the one they were proposing.

I'll have to do my sums carefully. We spend about £2k a year on heating oil (and that was before trump started playing the fool in the Middle East! If it stays as it is, we'll be nearer £2.7k a year. Octopus have a "cosy" tariff that's 13p / kWh for 8 hours a day, broken into three - (2 x 3 hour and 1 x 2 hour period). Really not sure how that's going to work with the EV as well. 36-40p at all other times and of course, 40p when you're going to need it most, in the early evening! As the wife is retired and I work from home most of the time, we're heating it all day, so it's not going to be a simple calculation.

The way you can make a time of use tariff work with an ASHP is by:

- having battery storage and charging it during off peak to get you through 1600 to 1900, and/or
- pre heating or rather essentially over heating your house during the cosy dips. This can be achieved by using a smart controller such as homely. You can input what tariff you have and the algorithms will do the rest.

The former would be much better for obvious reasons and we went for this option. We also incidentally started off with homely as well (not using the above feature though) but ended up taking it out as it had a mind of its own sometimes and did some random things. e.g. overshooting for no reason, not running a DHW reheat on occasion when it had been scheduled. That sort of thing.

 

[ericmark]

I find my house will cool 22ºC to 17ºC from 11 pm when heating turns down, to 8 am when heating turns back on, during the cold days of the year. So 9 hours it can drop 5ºC.

I don't like it warm when sleeping, or cold when awake, so only real option with a heat pump would be to sleep during the day.

 

[Avocet]

Do your research / due diligence on other forums: MSE has good stuff, perhaps SpeakEV where some EV users gamed battery / solar and cheap off peak slots (that made Octopus change their pricing of smart charging hours), and there will be others.

AIUI Only Intelligent Octopus Go (IOG) has the potential for daytime 30 minute slots for EV charging (none are guaranteed), plus the 6 hours whole house and 23:50 to 05:30... (but EV's can only charge for a total of 6 hours at the cheap rate in a noon to noon 'day').
IOG requires compatible EV (my Volvo isn't) and/or a compatible EVSE ("charger") my Hypervolt Pro 3 is.

Octopus Go is for non-compatible EV/EVSEs ... https://octopus.energy/smart/go/ and is at a fixed 00:50 to 05:30 so only 5 hours (whole house and EV).

Remember a 15kW OUTPUT heat pump will 'only' consume around 5kW (that Grant says 6.9 kW 30 A at full whack)... and probably less. Plus a home isn't gonna drop in temperature unduly in a few hours... and you have a wood burner (more than I have).

Reading suggests Tesla battery-inverters can safely 'island' a home during power cuts... Much more difficult to do with a generator in the mix (but anything is possible). All more expense of course.

Ah, OK, I'd misread your first post. Yes 5kW is a lot more manageable. (Still more than my little generator can manage, but not by much)! I agree that a house battery would be a good way to go in the long term.

 

[Avocet]

If you are with Octopus and have a smart meter you can download your 1/2 hourly usage for the base load / cooking / EV... and then use some 'averages' monthly/quarterly...

You need to work in kWh numbers rather than £s... £2.7k of kerosene would get 2,700 litres at £1 a litre or 27,000 kWh (roughly). At 80p you'd get more (33,750 kWh) ... and the rate is volatile with Trump's antics.

Octopus HP only Cozy: The 'killer' is their swingeing peak rate from 1600-2200 every day!! {For my Postcode a fix is 31.32p day / 15.36p cozy / 46.98p peak! variable is 26.67 / 13.09 / 40.01 - number will vary with Region.}

Octopus have a plethora of Time of Use tariffs... so worth looking at others (and other suppliers' tariffs in the longer term). If I put in that I have a compatible EV/charger and a HP Octopus suggest that Intelligent Octopus Go at 8p/kWh for 6 hours at night 23:30-05:30 and 34.32p/kWh day is the most likely one (only fixed rate is offered).

But you can use your own known kWh numbers for heating / hot water and allocate them to times of day to work out if a TOU tariff even works for you... Based on best guesses and advice from reputable installers.

Bear in mind that the 'rule of thumb' is to run 24/7 at two temperatures 'comfort' and 'set back' a few degrees lower, so the building fabric never cools right down. (Set back temp may never call for heat in some rooms). This means the HP never has to work flat out to reheat a cold building, and risk a poorer COP. (An MSE forum member matelodave lives in the fens with a similar wind chill issue you describe. I'd recommend you read some of his postings there).

I moved to Octopus in March anticipating going onto their Intelligent Octopus Go (IOG) EV tariff... and got a fix at 22.09p/kWh while the smart meter was accessible to them... It'd be more expensive to move to IOG than charge at the fixed rate pricing by my calculations.

I have an oil burner and a Heat Pump might make sense if/when my Grant boiler fails... but I'm still burning last year's 53p/litre delivery. We're 1000-1100 litres per annum (but use air to air heating in the shoulder months). Our electric use is much higher in Summer due to those A-A units cooling. I know I'll have to order kerosene in the not too distant future, so am keeping an eye on the price.

DO please get other Quotes and equipment recommendations from reputable local installers https://www.heatgeek.com/heat-pump-installers-liverpool-the-north-west

Update. I went on the Heatgeeks website and just initially, got an online quote. I was quite surprised at how much higher it was than Octopus, to be honest!

Heatgeeks
£5050 for a Vaillant aroTHERM plus 12kW heat pump and Vaillant uniSTOR PURE 150 L Standard water cylinder and two radiator upgrades.

Octopus
£1818 for a Grant Aerona 290 - 15.5kW heat pump and a 300 L water cylinder and 7 radiator upgrades.

(Both with the same £9k grant).

 

[Rodders53]

Are BOTH numbers just Guesstimates?
i.e. best guesses based on the limited info they both have on your home's heating and water needs - possibly from somewhere such as the last EPC, perhaps? Such that BOTH are subject to a (paid for) survey and room by room heat loss/gain calculations to refine what is actually needed (and the cost no doubt)?

Do both include the cost of removal and licensed disposal of oil boiler, tank, pipework including any kerosene left in the tank?

The 150 litre water cylinder is a tad small for a family home, and the 300 litre a tad large... So the two 'quotes' seem not to be "like for like" assumptions at all.

Octopus only seem to offer their own Cosy Heat Pumps up to 11.3kW heat loss and the Grant 15.5kW for larger, lossier homes... Not sure I'd be keen on their own brand (must do more reading on them in those other forums).

 

[drives]

@Avocet I'd be very tempted by that octopus quote- more emitter changes and a potentially significant saving in install costs to put towards a battery. I found heatgeek definitely at the more expensive end when we were getting quotes. We didn't go with octopus as they couldn't do a bespoke quote for us, taking into account that we already had a heat pump ready cylinder installed- otherwise we probably would have used them.

Furthermore you might find the grant actually modulates down quite well (comparable or maybe even better) than the vaillant.

I agree 150l cylinder seems way too small for a 220m2 house.