Anyone replaced a conventional gas boiler with a renewable energy source like airsource / ground source?

Looking at replacing an old natural gas boiler and wondering if a renewable system could be cost effective particularly since there seem to be some grants at the moment.

Also wondering if it will work practically given it’s not a new build the house is not going to be that thermally efficient and things like wet under floor heating are probably too invasive to retrofit.

My dad got rid of bottled gas and just got an electric combi.

It’s not cheap, but would be cheaper if he’d consider putting solar on the roof.

Looking at replacing an old natural gas boiler and wondering if a renewable system could be cost effective particularly since there seem to be some grants at the moment.

The long and short is no, even if you qualify for the grants, vs gas it’s a long way from being cost effective yet.

The grants we found were based on efficiency and frankly if you qualify for those you’d be better off using the 20k the ground source will cost in £5 notes to insulate your house.

Under floor wet heating these days doesn’t need to be invasive, carpets up, lay on floor seal and carpets back down is doable but obviously you’re raising the floor by about 40mm then.

Solar is good for heating if you’re well placed for it.

Really the reason for going to renewable is the eco side of it but it should be way down the list after insulation, insulation and more insulation.

We have a ground source heat pump for the main house and an air source for the flat. The house was totally refurbished with complete internal insulation, double glazing and new concrete floors with underfloor heating. The flat is a new timber framed building. We are in a rural location so no gas supply, would have to use oil or LPG.

Heat pumps work at lower temperatures than oil or gas boilers so are not really suited to a radiator system. You can use radiators but they would need to be increased in size to compensate. They work most effectively with underfloor heating as this uses lower temperatures than radiators

Costwise, it’s difficult to say as I don’t have anything to compare. It’s a 3 bedroom stone-built cottage in an exposed location in rural Aberdeenshire with a self-contained single bed flat attached. Everything is electric – heating, lighting, cooking, leisure use, so bills are quite high but I think it is probably cheaper than having to use oil or LPG.

It’s not cheap, but would be cheaper if he’d consider putting solar on the roof.

Well, not really I’m afraid – when you want the most heat the PV is producing very little in this country.
PV is good at heating a cylinder of water from March to October though.

the 20k the ground source will cost

An air-sourced heat pump system costs less than half that. we’re putting one in a new build, complete with underfloor heating throughout (no access to mains gas, so elec or oil is only other option). However, everything I’ve read says they aren’t good in old, poorly insulated houses – but in new (or heavily refurbished) homes, they are good. (and you get money back from the government every year – at least for now). We’re currently trying to decide whether to add solar (pv) panels to offset the electricity costs – there is supposed to be a new Feed In Tariff offered by all electricity companies from beginning of this year, but I’m struggling to find any real info about it!

(Having said that they aren’t meant to be good in old homes, my friend in Scotland has put one in his old drafty house, and claims it’s excellent)

Air source – no, just don’t go there. Unless you live in the warm south. Even still, probably not worth it.

Ground source can be good if you have a large garden area to put a large slinky in the ground. It’s most use is providing base heat to your house, i.e it’ll keep your house nicely at around ~17’C. Works best if supplemented with a wood burning stove or alternative to bring house up to “cozy” temps of an evening.

If you had, say an old farm house with a big grassy field / garden and no mains gas, it makes sense. If you have mains gas at ~3p kWh, then it likely won’t be the most cost effective solution.

Like running a bath, the most efficient starter is to first put the pug in. I.e. make you house well insulated before you look at alternative forms of heating.

Ground source can be good if you have a large garden area to put a large slinky in the ground

Can also be done with vertical bore hole

“Can also be done with vertical bore hole”

true, or if there is a mineshaft near by, or body of water with significant volume etc. However it is often easier and therefore cheaper to dig a series of 2m deep by narrow digger shovel width trenches in a grassy field.

However it is often easier and therefore cheaper to dig a series of 2m deep by narrow digger shovel width trenches in a grassy field.

Cheaper certainly but not easier in most cases as many houses are built so close together they’d make a Japanese rail commuter uneasy.

But yeah ours is going under the allotment.

Anyone replaced a conventional gas boiler with a renewable energy source like airsource / ground source?

The energy source for heat pumps is certainly “renewable”, but currently they will still cause CO2 emissions from electricity generation. The article below suggests that (based on 2016 electricity generation mix) use of a ground-source heat pump creates about 30-50% of the emissions of a comparable gas boiler system. Air-source pumps are less efficient.

http://researchbriefings.files.parliament.uk/documents/POST-PN-0523/POST-PN-0523.pdf

Parents had ground source heat pump put in their garden – seems to be good and keeps their house at a constant temp (via rads). It’s on all the time rather than a blast of high temp morning and evening. The only bad point is the pipe they had put in leaks if the ground dries out, a joint probably needs nipping up but they’re all underground with no access holes, so they just keep topping the system up now and again.

Always on – that sounds expensive?

The ball park quote I was given for ground source was £40k but I think that included a new hot water cylinder. the chap did say that the expected subsidy would be £30k.. No idea how realistic that is.

He also seemed to think gas would have duty applied to it to make it unattractive. Not sure how likely that is, banning new boiler installs is one thing but that’s a step further.

The other thing that gets thrown around is efficiencies. Gas boilers are 95% efficient and heat pumps are 400% efficient. How much are these Volkswagen stats though and in real world use will be wildly out.

What insulation is realistic for retro fit, we have cavity and 300mm or so in the loft, we could triple glaze.

Air source – no, just don’t go there.

Tell that to the Scandinavians who’ve been installing them for over 20 years.

Always on – that sounds expensive?

Depends on the operating demand of the system.

Gas boilers are 95% efficient and heat pumps are 400% efficient.

Ha! 400% is very definitely best case scenario. its been nearly 8 years since I last worked in renewables and back then, your average CoP was about 2.1 annually averaged over the seasons, meaning you harvested just over double the amount of energy that you put into the system. This ties in with a 50% reduction in CO2 compared to a conventional gas appliance.

If the system isn’t designed correctly, in the winter when you want the heat the CoP can fall below one, and it’s more efficient to run as an electric boiler, which is exactly what happens on some of them.

Devil is always in the design. AFACT there are less contractors just bashing them in and expecting miracles than there were, but you’ve still got to be careful.

The energy source for heat pumps is certainly “renewable”, but currently they will still cause CO2 emissions from electricity generation.

True, but electricity and gas carbon factors are about the same now, and a modern ASHP will deliver 300% efficiency compared to 90% for gas.

TL:DR

Has anyone mentioned or asked how we mainly generate electricity in this country?

As both ground and air source require electricity to help them along in the absence of geo thermal assistance or plentiful warm sunshine in winter.

Coal, or worse still imported wood pellet biomass i.e. Drax are used in significant quantities to generate and sate our unquenchable thirst for electricity, including charging the EV’s, lets not talk about how to deal with spent lithium ion cells.

Happy days.

Even a cursory google search shows that coal is only about 10% of our generation these days slackalice. Renewables generation is now more than double that and actually just beats nuclear as well. Gas is about 40%

I don’t mind a good bit of doom mongering, but do please get your facts correct.

wood pellets are good apparently – you can get a government grant for them 🙂 like diesel cars

They may be efficient (ashp), but when the air temp gets below 10 degrees, they are running like mad, with electric costs to match.
I work for a social housing company, we have a lot of air source, as well as a lot of ground source fitted.
The ground source are definitely the way to go, if you can dig a hole. The vast bulk of ours are put in by drilling a 300mm hole in the ground as far as it will go. I’ve got a feeling the Contractors only go as far as they want, rather than trying to get deeper for warmer earth.
There are a lot of complaints about the electric bill over the winter months, however, the systems do work, and the houses are always pretty warm.

If I was having mine done, I’d be going for ground source, with a vertical hole, actually, 3 or 4 holes would make more sense. Add in some solar panels to offset the electric cost, and it shouldnt turn out too expensive compared to gas.

think it’s nearer 3% science office, but agree with the sentiments.

OP – you really need to get a proper design done. ASHP will do much better COP than the 2.1 quoted (correct as of 6 yrs ago though). It will all come down to design. Did I mention doing the design right?

It will all come down to getting your room by room heat losses accurately calculated (and minimised), a proper heat emitter specified for each room and then a suitably sized heat pump sited. If you’ve got room to site a buffer tank, all the better. You will be really unlikely to be able to reuse your existing radiators – if you undersize the rads, the house will be cold and/or the bills huge.

yes I was thinking ground source sounds the most efficient but also with the biggest capital at stake. If it doesn’t turn out as expected. And presumably more holes is more expensive.

We’d have to go for the hole option as the garden wouldn’t be big enough for a surfaced based solution. I’d heard quotes of 100m deep which is pretty darn deep!

So we need the biggest radiators that we can fit into each room so that they can run at low temp.

or too big is bad too.

Not too bad as the thermostatic valve will limit the room temp – bigger than needed will speed up the room getting warm.

Get a design done by a professional with indemnities.

you mean so I can sue them if it doesn’t work? surely the small print will more than cover their ass

I know someone who had the vertical borehole ground source put in and they were delighted with it but a fair amount of up front cost. Also know people with air source who are very happy with that and people that got in time with roof top solar and very happy with that. North of Scotland. Been looking at self build for a while and air source seems standard but these are very energy efficient houses, no idea how it works with ‘normal’ UK houses.

do you know if those delighted people are switching from natural gas or from another energy source?

If you have mains gas and an older poorly insulated house then switching to air source would be a mistake in my opinion. Running costs will be comparable probably although possibly more than gas but install costs will be a lot different making the pay back questionable. Daytime electricity cost is nearly 3 times the cost of gas per kw so your system needs to be as efficient as possible which is why new houses and underfloor heating work well.

As has been mentioned, insulate, insulate, insulate, before you consider anything else. Also consider your controls and how you use them, see if you can run the heating a degree or more cooler, that could save you 10%.

If (big if) an air source or ground source is 300% efficient then in theory that levels the cost per unit of power playing field? Day 1 cost then is the deciding factor.

Whilst I see insulation is important, wouldn’t it’s presence simply lower the running costs of a gas boiler so in a comparison of which is cheapest both are benefiting from the insulation. Or is it the case that with little insulation an air source solution simply can’t generate enough heat to overcome the losses where as the conventional boiler can?

Or is it the case that with little insulation an air source solution simply can’t generate enough heat to overcome the losses where as the conventional boiler can?

This

I would also question just changing the boiler in terms of payback. You have to save a lot of gas to recoup the install costs. Of course if the boiler is proving unreliable then they become uneconomic to repair.

Like running a bath, the most efficient starter is to first put the pug in. I.e. make you house well insulated before you look at alternative forms of heating

This.

Insulation. Insulation. Air tightness. Insulation. Airtightness. Etc.

Then add in ventilation system.

A decade ago I did the maths on very simple house that was passive Haus level of insulations & airtightness, then fling in cheap as chips electric underfloor heating and solar panels for water. Over a 30 year lifespan, that was the cheapest route by a long way.

It didn’t score well on passive Haus or AECB, but in reality you would hardly use the heating and would be on a renewable tariff.

Please sort the building envelope to a very high standard before you go for fancy-pants renewables that cost huge capital, ongoing maintenance and shorter lifespan, with dubious performance at times.

@muddyjames

Always on – that sounds expensive?

But the rads are at a much lower temp (not so good for drying clothes), so it’s more of a constant gentle heat rather than a couple of blasts during the day

The current boiler is an 80’s model so replacement is necessary. really from an efficiency perspective. The rads are of a similar vintage with no convectors and so whilst replacement not essential they’re a bit tired now.

What are the steps for insulation and air tightness?

so your new boiler will be 90% efficient, old one 75% say. Saving you 15%, gas bill of 1000 per year saving 150?
Boiler install of 2000?
13 year payback?
Assuming new boiler is still working in 13 years and requires no maintenance.
Slightly simplistic way of looking at things but surely consuming less is the way that we need to go. Smart meters are a great example. Pushed to save energy when they don’t just make you aware of how much you are using. Aren’t we on generation 2 of them as well? Think the old analogue meters will be working for way longer than the digital equivalent…..

In terms of on going maintenance. I was under the impression that a modern condensing boiler can be basically be left to run without the need to service as long as you have a CO monitor until the circuit board or some other fancy item breaks. Whereas the floor mounted thing we have at the moment has a lot less to go wrong in it but I think needs regular servicing.

According to a website(!) the efficiency of the existing is a bit lower at 60% so a bit quicker payback.But along these lines I thought that installing replacement double glazing doesn’t really make sense from a financial perspective (assuming cost for windows is that which the man on the street pays, not someone fitting them themselves)

just need space for a compost heap…

https://www.instructables.com/id/Compost-Heating-System/

@muddyjames

If (big if) an air source or ground source is 300% efficient then in theory that levels the cost per unit of power playing field? Day 1 cost then is the deciding factor.

Not quite. At the moment, taking efficiency into account, GSHP are still more expensive to run than a gas boiler: https://nottenergy.com/resources/energy-cost-comparison/ That will surely change one day, but the gap isn’t closing and certainly much slower than the industry (and the guy promising you big financial gains) have been predicting for years. (And don’t forget: gas spend is way easier to predict than heat pump spend. It won’t be better than that table; it could be much worse).

And day 1 cost is returned over 7 years under the RHI. So even if you break even the break even point is years away. That’s a long time to be thousands out of pocket, even in an era of low interest rates.

RHI can work financially but I think you need to be in a weird house (in a way which adds up to big subsidy) and off-grid (so the comparison is to something more expensive than gas). There are good reasons to look for alternative heating arrangements. Money isn’t one of them (for now).

your average CoP was about 2.1 annually averaged over the seasons

spidey sense is tingling.

This was quoted to me as well when i had the folk round to quote for ASHP for my house – as we had a knackered oil system in the house from previous owners.

CoP averaged over the seasons – id have been as well fitting an electric boiler rather than ASHP because we simply dont use it over spring/summer/autumn so the CoP averaged over the time it was actually on was terrible

That coupled with the fact that i didnt want the boiler in the middle of my front garden where the installer wanted to put it – because if you stick them in a north facing wind trap they generally dont work very well ….. it was all based on grants from the government and by the time you had taken all the changes into account and paid to have the system designed and installed by the approved supplier it was a no brainer to stay on oil.

i went with oil and dont regret it. Id have gone bore hole if i could have but cost prohibitive.

CoP averaged over the seasons – id have been as well fitting an electric boiler rather than ASHP because we simply dont use it over spring/summer/autumn so the CoP averaged over the time it was actually on was terrible

Yep, and if you do the whole setup properly and have a really well insulated house and you add mechanical heat ventilation and recovery, you end up being much closer to not using any heating at all except in the winter, in which case why bother with a large capital outlay of the heat pump system in the first place.