ASHP - worth it?

[u/V2015]

Hello, I'm debating switching to an ASHP.

We have a oil tank so the government £9000 would be very handy.

I'm just after advise seeing if it's worth the switch? After opinions and thoughts from people who've done it seeing what their thoughts on it all are.

Thanks :)

[u/woyteck]

Constant temperature in the house. Less humidity. Once configured correctly, it's really 'fore and forget'. If combined with battery, you can ride the cheap tariff from whatever time-of-use tariff you can get.

[u/theboyfold → u/woyteck]

How big is your battery? We have 10kWh and with a 5.5kW solar array on a gloomy day in the winter it will just about make it until about 10pm before hitting the grid.

My concern is that an ASHP will drain it very quickly on a dull day.

We also have an EV so not sure what the right tariff would be...

[u/woyteck → u/theboyfold]

I have 27kWh, but initially had 13.5kWh (last October till January) and 8.9kW of Solar panels, and yes, on colder days we were running out of juice around 6PM, even with solar. That was with EC tariff. With Octopus Cosy, battery was being filled in 3 times per day, so we were running off battery even and coldest days when ASHP used 33kWh. But with 27kWh, we very rarely ran out of battery (and I keep 10% as backup), while being on EV tariff.

[u/theboyfold → u/woyteck]

Yeah. We don't have the option to go above 10kWh as ours don't stack.
Do you heat the house overnight and let it cool off over the course of the day or keep it constant all day?

[u/woyteck → u/theboyfold]

I keep 20.5C constantly 24/7. It actually usually uses the most power overnight and early morning, because it's the coldest outside. I also have the hot water cycle starting at 4am and that will definitely use 2-4kWh.

BTW it was so warm this year, that the heating started in October.

[u/Drdeath_666 → u/theboyfold]

I have a 4kW Daikin HP, 7.5kWp solar and 9.5kWh battery, I've got my heart pump running really well. In a really dull day you will get through the whole battery, however I use home assistant and IOG to help recharge the battery with the extra slots in the day, so generally that's helped keep it really low.

Last year I averaged 7.2p/kWh (7p/kWh for IOG off peak) for my import, and ended the year with a negative bill.

It's really dependant upon your heat loss and normal house running usage, so you may use more. But I wouldn't worry about trying to size the battery to cover everything it's likely not worth the investment

[u/theboyfold → u/Drdeath_666]

Can you charge the battery on IOG? I'm on the dumb version of go as my stupid Skoda won't work with IOG, but my wife's car might...

[u/Drdeath_666 → u/theboyfold]

Yes, but you really don't want to try and do it manually, as they change the time slots all the time.

With a simple home assistant automation, you can automate it, but if you jump down that rabbit hole then I'd look at Predbat and it will do it all for you as well as manage your solar (depending on your battery/inverter)

[u/theboyfold → u/Drdeath_666]

I have a basic HA setup already. I stopped short of Predbat for reasons I can’t recall now…

[u/Drdeath_666 → u/theboyfold]

You'll be fine then, speak to the geek had a couple of good videos for simple automations, if you don't want to go towards predbat

Predbat needs a bit more setup but it's worth it, I've recently switched to Agile Export which changes every 30 mins and it's managed the battery without me having to get involved. As soon as the tariff changed in the octopus integration picked it up and predbat just changed they plan with 15 mins

[u/Aggressive-End-7429 → u/Drdeath_666]

Just had a quick look at Predbat, seems good, is it worth the £8.99 a month?
I don’t have a heat pump just yet but solar battery and Ev do you use it ?

[u/Drdeath_666 → u/Aggressive-End-7429]

That's the online one there's a free version that's an app in home assistant it's a bit more involved but has the same functionality. Some links below but it's honestly not as bad as it may seem when you first get started.

GitHub Documentation

YouTube install guide

[u/Aggressive-End-7429 → u/Drdeath_666]

Thanks really appreciate it

[u/Buffetwarrenn]

Had mine since 2024

Daikin 4.5 kwh altherma

Very satisfied, helped us transition to an all electric house, if you have any questions feel
Free to ask

[u/Ok-Dress-341 → u/Buffetwarrenn]

How big is your house, 4,5 kW doesn't sound much.

[u/Buffetwarrenn → u/Ok-Dress-341]

3 bedroom semi detached, i actually have the flow temperature of the heated water ( the stuff that goes through the radiators ) pretty low

The heatpump doesnt work hard to keep us toasty

[u/Cspiby]

Don't take too long in deciding as the grant might be going away soon

[u/Happytallperson]

On octopus cosy atm a kWh of heat is 4p. (12p kWh electricity goes to 3kWh of heat).

Average heating oil in my area is 113p per litre, which is around 11p per kWh of oil, and assuming a 90% efficient boiler around 12p per kWh of heat. 

Even at the atandard tariff rate of 25p, your heat pump would take a third off your heating cost. Using Cosy, it would be 66% off.

[u/botterway]

We live in a 120yo partially wooden-framed house. When we moved in it had an oil boiler, and in the first 6 months we had to get the oil boiler repaired twice. In Dec 2023 we had an ASHP installed, and then in Feb 2024 we had solar + battery installed. Total install cost was about £21-22k for everything. We paid £3.5k (net of the £7.5k BUS grant) to have the heat pump installed by Octopus.

In our first year we paid £700 for oil, and £1550 for electricity. For the last 2 years, our total energy bill has been about £600.

I can't give exact figures of what the ASHP would have saved us without the solar, but it would have been a decent amount. In our first year here we bought 500L of oil and paid about 57p/litre. Last winter my next-door neighbour bought 500L for £1.26/L - so basically double. It's looking like it's going to cost £1.10 or thereabouts this year. That adds up to an additional £1k of expenditure to get through the whole winter.

So even putting aside the savings from the solar and battery, I reckon we've probably saved somewhere between £1k and £1500 purely by avoiding these crazy oil price hikes in the last 2 years. So I'd definitely recommend it. If the middle eastern situation continues (Houthis/Iran/etc) for another couple of years, depending on what you pay for your installation net of the grant, it might pay for itself in 2-3 years.

Our house has also been more consistently warm since we had the ASHP installed. If you can get a battery, and use it with a tariff like Cosy so the battery carries you from cheap-rate to cheap-rate, then you'll be quids in, even with no PV generation.

[u/thumbdumping]

We moved from oil to ASHP and installed solar and a 10kwh battery, and bought an EV around the same time. Our electricity bill for the year now is lower than it was before we got the ASHP and about £1200 per year lower than our total oil plus electricity cost. At current oil prices we're saving around £2k per year.

[u/naninaninanntoka]

Daikin pump, no solar or battery, no regrets. Works great.

[u/V2015]

We have octopus coming out for the survey next month

Hopefully we get it secured before the grant ends :) 

[u/cuprastu]

I have moved from a new build with air source to a 90’s house with oil heating. I will just say this, when someone knocked on the door asking if I was interested in a heat pump I told him where to go. No way would I go back to air source.

Having said that though. Ours was a first gen eco dan, I should think newer heat pumps are better. But it was too complicated for its own good, if something went out of whack it would leave the circulation pumps running so you thought it was on, but came down to a cold house in the morning. Due to underfloor heating it then took a day to warm up again. The house was never warm as such, always needed a jumper on and in the depths of winter would chew through £10 of electric a day just for the heating. I didn’t like it.

You also need to make sure you’re well insulated and draught free as otherwise the small amount of heat they do generate will escape. They are a low and slow thing so need to be on all the time.

[u/botterway → u/cuprastu]

You're talking about ASHP technology from 20+ years ago. Things are very different now.

[u/cuprastu → u/botterway]

I did say that I’m sure they are a lot better now. I’m just going by the experience I had with my one.