Air source heat pumps

Psycho Sonny · 1 Jul 2021 at 14:53

Okay background info.

My boiler is 20-25 years old. So on its last legs or who knows maybe it outlives us all?

I can get a 100% loan for the heat pump that is 0% interest free. So I do not need to pay out of savings.

I can then get 75% cash back on my purchase paid into my bank account.

This is a Scotland only initiative.

So if I pay just 25% and it's interest free. Is it worth doing? I will also be paid the RHI so I'm thinking this will actually make me money by doing it.

My home is pretty well insulated built 20-25 years ago. Has floor, loft and cavity wall insulation already.

Thoughts?

Tom_ed1987 · 1 Jul 2021 at 19:22

On those numbers, i'd say yes. What's the detail of the RHI?.

But bear in mind the 'hot water' you get out of an ASHP is nowhere near as hot as that out of a boiler, so you need big efficient radiators or UFH, & the system essentially on 24/7 for it to work properly.

They also seem to be a bit unreliable especially once the outside temperatures drop, anecdotally at least, so I'd make sure you keep a backup electric immersion & maybe some cheap electric heaters.

Shoeyuk · 1 Jul 2021 at 20:18

The landlord put it in our place the only annoying thing I find is it can do the heating and the water at the same time.

Dangerous Dave · 1 Jul 2021 at 20:53

With electricity edging up to 8 times more expensive than gas you need to do the sums. Even with the system working at peak efficiency you’ll still be paying double your gas bill. Come sub zero temperatures the efficiency drops off.

You’ll need to size your radiators for a flow temp around 40c which is roughly double the size from the 70c ish from a boiler setup in the 90s.

For hot water you’ll need a tank preferably an unvented cylinder for mains hot water and to get that up to 60c it will be supplemented with a immerser heater. If you use a lot of hot water this gets expensive quickly. My 300l cylinder costs approx 40p to heat with gas if I did that with electricity (it would be cheaper with a heat source pump supplementing the immerser) it’s approx £2.50 and I’m still on a 14p per unit rate new rates are quickly heading to 20p

b0rn2sk8 · 1 Jul 2021 at 21:54

This looks far more generous than the UK scheme which was basically an upfront payment of the RHI so it just completely fell short of what was needed for ASHPs.

I had a quote for a ASHP and it broke down to:
£8k for the heat pump and installing a cylinder, associated heat controls, electrical, plumbing and gas work.
£2k to upsize 10 rads.

I guess it depends on what the 75% actually applies to, if the 75% only applies to the unit itself then that obviously cuts down significantly how much you'll get back. But if it includes all the work like upsizing rads then it suddenly looks far more generous.

I think the RHI works out to a large % (possibly 75%) of the estimated heating costs over 5 years but electric was cheaper back then.

Really you need to do a total cost of ownership calculation over 10+ years and see where it it fully costs out to compared to a modern boiler. A straight boiler swap will be around £2.5k. Your EPC will tell you your estimated energy needs, base the calculations from that to make it comparable.

I expect it will be fairly close costs wise so it may be worth it.

BigBoy · 1 Jul 2021 at 22:24

Unless you live in a hyper efficient fairly new property it will not be worth it. The systems are primarily designed around a positive pressure property, most existing homes are equal or negative pressure.

tonys · 2 Jul 2021 at 12:23

We have a heat pump on a extended 3 bed semi(1930), we used £364 in Dec-Jan, approximately £125 autumn-spring months and £77 last month. That is all electric no gas or oil, we get a payment of £322 per quarter from the RHI for 7 years. The unit we have is an LG Thermo V, which has had to be fixed below one of the bedroom windows as it couldn't go on the ground because of flooding when it rains heavily. Be aware that it does sound like a washing machine on a fast spin cycle when it ramps the fans up and does vibrate on the wall a bit

We are in Northamptonshire

Psycho Sonny · 2 Jul 2021 at 13:11

Dangerous Dave said:
With electricity edging up to 8 times more expensive than gas you need to do the sums. Even with the system working at peak efficiency you’ll still be paying double your gas bill. Come sub zero temperatures the efficiency drops off.

You’ll need to size your radiators for a flow temp around 40c which is roughly double the size from the 70c ish from a boiler setup in the 90s.

For hot water you’ll need a tank preferably an unvented cylinder for mains hot water and to get that up to 60c it will be supplemented with a immerser heater. If you use a lot of hot water this gets expensive quickly. My 300l cylinder costs approx 40p to heat with gas if I did that with electricity (it would be cheaper with a heat source pump supplementing the immerser) it’s approx £2.50 and I’m still on a 14p per unit rate new rates are quickly heading to 20p

I already have solar panels and they will give me an interest free loan to get battery storage which will then open me up to free energy during summer and cheap off peak charging hopefully when I switch next year for when the battery isn't being topped up by solar. A lot of companies now offer a cheap rate during off peak hours and peak hours I would hope solar and battery takes care of those.

b0rn2sk8 said:
This looks far more generous than the UK scheme which was basically an upfront payment of the RHI so it just completely fell short of what was needed for ASHPs.

I had a quote for a ASHP and it broke down to:
£8k for the heat pump and installing a cylinder, associated heat controls, electrical, plumbing and gas work.
£2k to upsize 10 rads.

I guess it depends on what the 75% actually applies to, if the 75% only applies to the unit itself then that obviously cuts down significantly how much you'll get back. But if it includes all the work like upsizing rads then it suddenly looks far more generous.

I think the RHI works out to a large % (possibly 75%) of the estimated heating costs over 5 years but electric was cheaper back then.

Really you need to do a total cost of ownership calculation over 10+ years and see where it it fully costs out to compared to a modern boiler. A straight boiler swap will be around £2.5k. Your EPC will tell you your estimated energy needs, base the calculations from that to make it comparable.

I expect it will be fairly close costs wise so it may be worth it.

Won't include radiators just the heaty pump and associated installation costs.

BigBoy said:
Unless you live in a hyper efficient fairly new property it will not be worth it. The systems are primarily designed around a positive pressure property, most existing homes are equal or negative pressure.

I've already stated I'm in a fairly new property (20 years old) and it's been loft, cavity and floor insulated.

Saying that I could probably do with my windows being re-sealed but other than that it's fairly good at being warm and my bills have never been excessive.

SpeedFreak · 21 Jul 2021 at 16:18

Timely conversation. My 25 year old boiler is now shot and needs replaced. 4 bed detached insulated pretty well, but certainly not comparable with modern standard. I have a wife and three kids. The options are:

1. Straight swap the system boiler and keep the vented water cylinder £2k.
2. Install a combi boiler £2k.
3. Install a new system boiler with unvented cylinder - £4k
4. Install air source heat pump and unvented cylinder - £10k less grant over 7 years of c. £8k. but also need new downstairs radiators - £2k

I have ruled out 1 and 2 due to family size and the current frustration with having a vented system. We are planning an extension/renovation next year and will likely be adding underfloor heating downstairs, so would preferably sort the boiler at the same time but the current one is completely shot so waiting is not an option. I would like to go for option 4 with the view to adding a solar array and battery storage next year, but am wondering if I should just go for option 3 for ease.

Any thought are welcome.

BigBoy · 21 Jul 2021 at 16:53

SpeedFreak said:
Timely conversation. My 25 year old boiler is now shot and needs replaced. 4 bed detached insulated pretty well, but certainly not comparable with modern standard. I have a wife and three kids. The options are:

1. Straight swap the system boiler and keep the vented water cylinder £2k.
2. Install a combi boiler £2k.
3. Install a new system boiler with unvented cylinder - £4k
4. Install air source heat pump and unvented cylinder - £10k less grant over 7 years of c. £8k. but also need new downstairs radiators - £2k

I have ruled out 1 and 2 due to family size and the current frustration with having a vented system. We are planning an extension/renovation next year and will likely be adding underfloor heating downstairs, so would preferably sort the boiler at the same time but the current one is completely shot so waiting is not an option. I would like to go for option 4 with the view to adding a solar array and battery storage next year, but am wondering if I should just go for option 3 for ease.

Any thought are welcome.

Go 3 it will be fine in the long run!

danoliver1 · 21 Jul 2021 at 17:00

b0rn2sk8 · 21 Jul 2021 at 17:42

Honestly? Option 3 would be where my money went at the moment.

I’m surprised that only the ground floor rads would need replacing, I would have expected all bar the smallest rooms would need upsizing. Spending £2k ripping out the old rads and replacing them with new ones to then rip those out and replace them with underfloor heating shortly after seems like an inefficient use of funds.

It’s also my understanding that when you get the heat pump installed is some of that install cost goes towards putting in an unvented cylinder. So eventually when the requirement does come in that you must get a heat pump, some of that work will have already been completed if you went option 3.

I’d expect the heap pump to have higher running costs in the short term, electric prices are nearing 5x that of gas now and heat pumps are less efficient in the winter when you need them.

It’s also worth considering that unless you can get a massive solar array, it’s unlikely you’ll generate enough power to charge the battery to cover evening use, re-heat your hot water and then make any meaningful dent in your heating bill come the winter.

If it were me, right now, I’d put a heat pump at the bottom of my list of environmental measures.

You really need to do everything you can do to retain heat in the property before going down this route. That covers windows, insulation (walls, floors and roof) and heat recovery ventilation.

I’d certainly prioritise solar over a heat pump and I’d add a battery if it made sense to do so. Id make sure that the solar is integrated with the electric tariff, battery, hot water cylinder and electric car to make sure I was maximising it’s potential (e.g. zero export to the grid).

SpeedFreak · 21 Jul 2021 at 18:34

Thanks gents, helpful input.

Tom_ed1987 · 21 Jul 2021 at 19:29

I'd just swap the boiler and keep the vented system, with perhaps a bigger HW tank if you need it (pretty cheap vented) - why wouldn't you? It's the cheapest, most reliable, tried and tested & most flexible.

A solar array/battery storage does not make any financial sense & solar won't do much to blunt the running costs of an ASHP over winter. It's great in the summer if you for AC tho

tonys · 21 Jul 2021 at 19:41

You can't run an ASHP for air con as you get the money back from the government, just for using as a source of heat only. What you do after the end of the scheme would be up to you.

b0rn2sk8 · 21 Jul 2021 at 20:43

tonys said:
You can't run an ASHP for air con as you get the money back from the government, just for using as a source of heat only. What you do after the end of the scheme would be up to you.

Well almost all air source heat pumps used in central heating and hot water systems are 'wet' systems anyway so they can't be used for cooling regardless. They are only designed to heat the water that goes around radiators/under floor heating and hot water cylinders. They have no ability to produce cooled air.

Centralised forced air systems are extremely rare in the UK.

tonys · 22 Jul 2021 at 00:48

The unit is just an air con unit wired so that it only heats with associated pipe work, so I was told by the installers.

dirtychinchilla · 22 Jul 2021 at 16:32

Don't do it. Your house is not set up for running at low flow temperatures. As had already been said, you will have to replace every heat emitter in your house. Not only that, but you are used to demand controlled heating i.e. you need heat, you generate it. Heat pumps are massively subject to the weather outside. The coefficienct of performance is massive affected by the external temperature and flow temperature, and so your COP drops in the winter when you most need heating. It will then cost you a boat load more in electricity than gas ever cost.

And, it's not necessarily any greener. Yes, you will be able to get some electricity to power it from your solar panels (probably), but the rest of the energy will have to come from the grid. And guess what, when your solar panels aren't generating, nor are anyone else's. Gas is consistently cheap, and is used in power stations to generate our electricity.

Get a decent boiler, get good TRVs (Danfoss) with good heads (also Danfoss), reduce flow temperatures, balance your heating system, and you won't have to worry about any of this BS.

Heat pumps are unlikely to be the future. Heat networks will be.

tonys said:
The unit is just an air con unit wired so that it only heats with associated pipe work, so I was told by the installers.

That's a gross oversimplification. A heat pump is a device that transfers energy from one medium to another, so in this case air to water. It does it in a fashion which means you can essentially get more energy out of it than you put in i.e. 1 kW of electricity might lead to an output of 3 kW of hot water.

PermaChanged · 22 Jul 2021 at 16:57

We're looking in to getting an air source heat pump too, due to the fact we're looking to install a wet underfloor heating system throughout - the energy coefficient of them seems pretty decent, and Guernsey winters aren't quite as cold as those within mainland UK so seems a worthwhile investment. Also clears the clutter and eye sore of having an oil tank in the back garden too.

b0rn2sk8 · 22 Jul 2021 at 17:14

I agree it’s a different conversation if you already have underfloor heating, a well insulated property and no access to gas. It does help if you live somewhere a bit warmer but the coefficient of performance only drops off when it’s really cold which in reality is only a few days in England. Most days in winter are well above freezing and it rarely dips below -5c for any length of time.

Slightly different if you live in the very north of Scotland or up a mountain but few do.