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Author Topic: The Green Homes Grant scheme - is it worth it (oil to heat pump)  (Read 741 times)
myozone
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« on: October 14, 2020, 12:05:42 PM »

Just been looking into the new Green Homes Grant scheme and wondering if it's really worth it. We've currently have an oil combi boiler (~9years old) and oil at the moment is about ~28 pence a litre which works out to be around 4 pence Kwh less inefficiencies. Even the Octopus Agile tariff would come nowhere near that, so on paper it looks not a goods idea to change - other than more green of course.

Any thoughts ?
« Last Edit: October 14, 2020, 12:24:39 PM by myozone » Logged

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GarethC
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« Reply #1 on: October 14, 2020, 12:15:09 PM »

Unfortunately (and other will know better) the decline in oil (and gas) prices relative to electricity has given the economics of heat pumps a kicking I think.

When electricity was three times the cost of gas per kWh, there was a chance of at least equal heating costs (with a system performance factor of 3).

With electricity now costing at least four times as much as oil and gas (if I recall correctly), a heat pump will almost certainly lead to higher running costs I think.

But they are now -much- greener than an oil boiler, as the electricity powering them is at worst gas fired (well almost always), so the associated carbon intensity is really low.
« Last Edit: October 14, 2020, 12:17:16 PM by GarethC » Logged
myozone
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« Reply #2 on: October 14, 2020, 12:23:22 PM »


That's more or less my thinking. I'm in West Cornwall and it never getting 'really cold', and even being very generous to heat pumps (COP of 4) at the moment the costs are about 30%-50% more expensive than oil. It sort of feels the right thing to do going to a heat pump, but economics make it a lot more expensive.
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Countrypaul
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« Reply #3 on: October 14, 2020, 12:40:12 PM »

I suspect it will depend on how much heating you actually need, and whether you are looking at GSHP or ASHP.

If you only use a relatively small amount of oil, the servicing costs of the boiler will make a significant contribution to the annual overall cost. How much oil do you currently use? Do you know how much is for DHW compared to background heating?

What sort of heat emitters do you have in the property, if the heating system can run at 30C the the heat pump COP is likely to be much higher that if it needs to run at 50.

Also, would you also be elegible for the RHI on your heat pump install? I found that the RHI over 7 years should pay for the cost of the heat pump. Slightly different situation since far various reasons I we just ran on immersion heaters for teh first 12 months - but that did give us a basis for the actual amount of heat we needed. We also run our ASHP mainly on E7 so that drops the price of the electric to around 9p/KWh so heating should be around 3p/KWh I believe (will only find out for certain this winter!).

Do you have a PV system installed with a diverter?

Just comparing the initial outlay and fuel costs might give you a totally different result to that obtained by looking at the other incidental costs.
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Pile-o-stone
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« Reply #4 on: October 14, 2020, 02:21:34 PM »

We're trying to do a fabric first approach and so applied for a grant towards installing (more) internal insulation. 10k should do a few rooms and I'll finish of whatever is left myself. If you need to upgrade your insulation then that'd probably be more cost effective on your bills than fitting a heat pump.

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brackwell
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« Reply #5 on: October 14, 2020, 07:48:43 PM »

You ask a simple question for which there is not a simple answer without a lot more detail particularly of the premises,occupants and life style. 

Heat pumps are known to favour very well insulated houses generally with underfloor heating which is not the image i have of the average Cornish house.

The difference in running costs is unlikely to be worth it, however should your oil boiler break down then that MAY be the time to change. I doubt these grants are going to go away quickly as we strive to 2050.   I guess you realise that you most likely would have to remove the oil boiler if you went for the grant.

My approach would be to keep the asset value of the boiler for "beast from the east" moments but do everything to minimise its use and certainly not to heat water in the non CH period.

Do you feel already fully insulated with no draughts and blocked off chimneys if you have them for eg.
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myozone
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« Reply #6 on: October 15, 2020, 05:33:45 PM »

Sorry I've been away for a while,

We use around ~680L (the last two fills have been exactly 683L!) of oil per year and around 1950 Kwh of electricity. The heating this time of the year is a 'One Hour' press when it feels cold <17 ish. When it's colder, half hour in the mornings an 2-3 in the evening. 5 Rads with a 25Kw boiler and ~80M2 bungalow. Boiler service about 65 (It's not been done for over 2 years).

I've no idea about RHI - how do I find out.
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marshman
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« Reply #7 on: October 15, 2020, 06:11:56 PM »


I've no idea about RHI - how do I find out.

You need to get an EPC done, unless you have a recent one.  This will give you a calculated annual heat "requirement" figure. This figure combined with the SPF  (Seasonal Performance Factor - calculated from the new heat pump install) will give you the number that your RHI (Renewable Heat Incentive) payment will be based on.

The problem is as others have already pointed out heatpumps are best in well insulated houses with large heat emitters which can run at low temperatures - ideally, but not necessarily, underfloor heating. If you already have these then the EPC will most likely, but by no means certainly, have a lowish annual heat requirement figure, this in turn leads to a low RHI payout. So to maximise the payout you want a draughty old house with high heat demand. Problem is to qualify for the RHI you need an MCS certificated system which has to comply with all the rules and regs, one of which is that it must be designed to cope with the heat demand and keep all the rooms nice and toasty even on the coldest days. This can lead to an oversized (and over priced) system.  Not an easy path to navigate. I struck lucky as I live in an old property and lots of assumptions (incorrect ones) were made as to its construction resulting in an absurd EPC figure - I did argue it at the time (silly me!) not realising that it was in my favour, but the guy wouldn't budge (thankfully!). I did end up with an over sized heatpump, but it does heat the water quick and is stupidly cheap to run, but the RHI covered the cost in a little over 4 years, in my case it was a no brainer.

For your situation I think you need to do some more work - try estimating your EPC figure and the look around and see if you can guestimate the SPF which will give you all you need to see how much RHI you will get, it is based on the flow temperature you need to run your system. The SPF MUST be above 2.5 to qualify for the RHI so you could use this as a minimum worse case figure.  You could then get a couple of quotes from local installers (must be MCS registered) and then you will have the economic figures you need.

My gut feel is that it won't work for you but I could be wrong.

Roger
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Countrypaul
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« Reply #8 on: October 15, 2020, 10:58:07 PM »

If you look on the site: https://www.gov.uk/guidance/apply-for-the-green-homes-grant-scheme it explains the Green homes grant and RHI and how they are related. The green homes grany fnishes in March 2021 I believe and you need any installation finished before it ends to qualify.

My experience with getting an MCS certificate for RHI was similar to Roger's story. The assumptions made in the process did not reflect reality with the result that the figures generated were far worse so I ended up with a larger than necessary ASHP. In our case we have a thermal store (430L) so the HP does not short cycle (which kills heat pumps evidently) but it does heat the sotre up quite quickly. If you look back on this forum you wil probably find a thread about the EPC and that ist seems to bear little reemblance to reality.

The RHI is based on figures from the EPC and needs to cover a wors case scenario, which means it needs to be able to provide all the heat needed to keep the house warm (can't remember the figure but something like 21C for living rooms, bathrooms and kitchen, 20C for bedrooms, 16C for Hallways etc) when it is -3C outside. In our case the calculated value came out at 10.8KW (iirc) even though other calculations and experience had shown that the house performed much better - as a result we have a 11.2KW Ecodan ASHP.

680L of oil is quite low, I used to use about 1000L a year in a 90m2 semi - but then it was solid walls and no insulation on the floor or walls.  I ran the same oil boiler for 25 yrs because whenever I looked at the costs of replacing it, it always seemed to work out better to wait until it expired which it never did (unlike most nwe combis from when I have seen posted on here)

Current house is about 225m2 with UFH and requires less heat than the old one - although with two computer game made boys we do seem to have a high background electricity use!
You mention 5 rads with the Oiler, if you changed to a heat pump they might need chnaging to larger ones to output the same heat at a lower temperature, alternatively, you would need to run the heat pump for longer periods to get the same amount of heat out at the lower temperature. Running a heat pump for a longer time at a lower temperature is the most efficient way to run a heat pump but is a complete change in attitude and concept for those used to a boiler.
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myozone
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« Reply #9 on: October 16, 2020, 11:14:39 AM »

To put some meat on the bones, the house a 70's bungalow with filled cavity walls - not that well by all accounts, double glazing and >200mm roof insulation. The boiler replaced night stores around 9 years ago - we've been here 10 years to the day on Sunday(EPC then but says expired when I looked it up). What I'll do is a have a local (accredited) installing come and give a quote and see what they say. My feeling is new rads and a 'small' air source heat pump but I'd doubt it would save any money and probably I'll stick with oil until at least something major goes wrong with the boiler.

Out of interest, I guess the 15mm piping would remain the same with a heat pump at a lower system temp, but maybe a faster flow rate?

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Countrypaul
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« Reply #10 on: October 16, 2020, 01:12:10 PM »

To put some meat on the bones, the house a 70's bungalow with filled cavity walls - not that well by all accounts, double glazing and >200mm roof insulation. The boiler replaced night stores around 9 years ago - we've been here 10 years to the day on Sunday(EPC then but says expired when I looked it up). What I'll do is a have a local (accredited) installing come and give a quote and see what they say. My feeling is new rads and a 'small' air source heat pump but I'd doubt it would save any money and probably I'll stick with oil until at least something major goes wrong with the boiler.

Out of interest, I guess the 15mm piping would remain the same with a heat pump at a lower system temp, but maybe a faster flow rate?


I think the 15mm pipe may well depend on what the layout is. If it is a single 15mm pipe that runs around all radiators that may be too limiting for the high flow rate the heat pump may require. It there is say a 22mm backbone and just 15mm drops to/from each radiator that would make a significant difference.

Have a look at the RHI, as that aims to pay back the cost of instaling the heat pump over 7 years (so it effectively costs you nothing).  If the cost for the ASHP install was say 8500, and you got a 5000 Green Homes Grant, then the RHI woudl pay you 125/quarter (index linked) over the next 7 years. Without the grant the RHI would pay you around 300/quarter.

I have no idea whether larger radiators and changes to piping would be included(logic says yes as they are required but...).

If you model the costs, beware that E7 can be more expensive for "normal" daytime electricity than a standard tariff, so if you run your heat pump in the evening rather than overnight it could work out more expensive.

I ended up with a large spreadsheet containing various models that we used, but since we were renovating and removing the old open coal fires, the oil boiler and the electric storage heaters (yes all 3 types here presviously) and putting in some decent insulation as well as extensions, I was effectively starting from a blank sheet of paper regarding the heating system.
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brackwell
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« Reply #11 on: October 18, 2020, 01:18:52 PM »

I wonder if you have considered a wood pellet boiler ?  Green, as cheap as oil, RHI grant available i think?

Ken
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myozone
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« Reply #12 on: October 19, 2020, 09:49:53 AM »

I wonder if you have considered a wood pellet boiler ? 

I have, but no room for a store/hopper, the external oil boiler now is a bit in the way.
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