Air Source Heat pump and solar to replace oil boiler

I’m looking for some advice regarding what to do about the almost 30 yr old oil fired boiler in my house.

It is not without its flaws and I’m reluctant to wait till it dies and then have to rush into repair/replacement (inevitably in the depths of winter!) so I’ve recently looked into the costs of replacing it with an air source heat pump plus a 5.6kw (south facing) solar array and have found an installer I’m happy with, but am in two minds about whether it’ll end up costing a fortune to run!

The house is quite large~270m^2, with underfloor heating on the ground floor and radiators upstairs. Including in the quote is replacement of all rads with larger ones to allow for running both heating circuits at a lower temp, as well as a new hot water cylinder.

Does anyone have any experience of making a similar change? Or can anyone point me to a simple way of using the fact that I tracked oil consumption last winter to estimate how much it might cost for a similar amount of heating from an air source system??

Any insulation ? It’s going to cost lots to run. The insulation will lessen the blow.

Out of interest why air source and not ground source? I was under the (possibly mistaken) impression that ground source just involved a borehole now and was better in winter as the ground is always above freezing a few feet down.

Air source and ground source only are really worth installing in new very well insulated homes, they very rarely are a wise choice in older properties

Out of interest why air source and not ground source?

Cost I’d imagine.

Similar here, I had an epc done so asked the assessor what he thought about an air source heat pump.  Only good on new builds, I d have to spend so much on insulation, new rads it’s not worth it.

House has access to under floor so he did say get that insulated, as well as more in the loft.

Don’t know if they are still doing it but Skipton building society were doing epc s for free, no catch, if so just open an account with a quid and get one.

Ground source either need a 10m bore hole(s) or large enough ground area for a series of trenches if you can’t go vertical – neither option is cheap.

Air source are great until you get to around/below freezing then the efficiency massively reduces – less than 1:1 when going into defrost cycle.

Plus you’ll need newer bigger rads (about 30% bigger) as the system runs at a lower temp than a boiler.

You could offset with solar PV and battery storage – but not going to be cheap.

House was built in 1996 and is quite well insulated in theory (cavity wall insulation, triple glazing, >200mm loft insulation) but I spent last winter (our first in the house) chasing drafts where things weren’t quite right (gaps around some exposed timbers, flush spotlights fitted in a pitched roof), so while it’s not a period property with leaky sash windows, it’s not perfect!

Putting aside the variability of the solar, is it possible to convert the quantity of oil used last winter to an equivalent energy input and figure out how much the same amount of energy input from a heat pump would cost for a given electricity price? Or does the varying efficiency as external temps drop make that too complex a set of equations for a meaningful comparison?

Trying to offset electric heating with solar PV in the UK would be like throwing a sausage up sauchiehall street.

Some of the numbers being quoted by air pump users on the PV forums are eye watering.

My old man has 8kw of solar PV tracking the winter sun and he is in the middle to south of France and it doesn’t even touch the sides with his air source heat pump and the 2 thermodynamic tanks

I understand that air to air heat pumps are very efficient but they only provide heating and require a separate hot water solution

@trail_rat that’s why I suggested battery storage (but you’d need a lot!).

Whoever told the government that air source heat pumps are the way forward wants shooting…..

As said better for new homes but still not all it’s cracked up to be.

We generally advise clients if they have gas to their property to keep going with it – you can cheaply swap the burners when it changes to hydrogen mix.

With oil or tanked gas it’s a bit of an awkward one…..

@dc1988 they’re efficient as long as there is heat to take out of the air.

The less heat it can extract the more it has to put in via the electric heater.

Typically they quote about 3:1, but as you get closer to and below freezing then it’s pretty much 1:1 as the heater is doing all the work.

You can get heating & hot water – Mitsubishi do a combined system. It still requires an immersion heater though in the cylinder same as a conventional system.

I enquired with a company that installs heat pumps with the view to replacing the 15-year-old oil boiler in my house.

Conclusion was that it’s possible but expensive, and if I wanted to do it on environmental grounds then changing to HVO is a much better bet.

With batteries you can shift most of your energy use to off-peak times (so purely resistive heating of hot water, and some use during the day).

Do not expect anything realistic from solar in the winter months. Mine covered hot water from March – November but the batteries were being topped up from the grid to handle everything else.

£22000 to replace our oil boiler with ASHP for including all the required conversion to 15-22mm pipe work. That doesn’t include the costs to re lay the floor, sort everything out.

Crikey.

but as you get closer to and below freezing then it’s pretty much 1:1 as the heater is doing all the work.

This is just not true. There is still plenty of heat in the air, just because it’s gone below the temperature at which water freezes doesn’t change much. Your freezer wouldn’t work otherwise, that’s extracting heat from -18C.

At low but above zero temperatures it can require an occasional defrost cycle to remove frost buildup. As it goes below zero it shouldn’t need to defrost as much or at all because there’s less moisture in the air to freeze. The SCOP of a properly designed system should average above 3 over the winter season. Research has shown they can work in all housing types; the biggest problem is normally finding space to put the outdoor unit. Air-to-air units won’t do hot water, but air-to-water systems (ie. radiators) will. Our solar PV couldn’t run our A2A units on its own all winter but still provided a worthwhile contribution over the darkest months; in the shoulder months before about November and from about late February they provided the majority of the power needed for all but a few cold, dark days.

Ground source either need a 10m bore hole(s)

Boreholes for vertical GSHPs are normally waaaaay deeper than that, 100m is more likely. They are more efficient as the temperature is more constant but very expensive…

Our intention is air to water heat pump providing ufh and dhw.

Europe seems to be well ahead of American manufacturers so should be some decent options.

Can be below minus 10deg through the winter for short periods but seems like a reliable solution on the american north west coast

Sounds like you’ve got a new build with microbore pipework feeding rads. A real problems as most new build of the last 25 years are like this.
Heat pumps can heat any property the design is critical though. If a building which is poorly insulated  needs 20kw it doesn’t matter which way of delivering it you use it will be expensive and worthwhile exploring some extra insulation.
The problem is if people fit heat pumps to these properties and don’t undertake a proper system upgrade then you are going to struggle as you can’t actually deliver 20kw at the low flow temp required.
It will be interesting to see what comes on the consultation to remove the wholesale price of gas being linked to electricity cost.

The general rule of thumb is that for horizontal GSHP, you need 3* the footprint of the house in available land. And for vertical GSHP, you need a number of boreholes, 100m deep equal to 2x the sqm/100 of the house. So my house is 170sqm, I’d need 3x 100*.015m boreholes. My last quotes for this were £19000 just for the boreholes.

Daffy – that’s too general as the insulation levels could differ hugely.

That average was based on current UK housing stock.

Obviously new builds and different parts of Europe will differ. I’m also told that there are difficulties with ASHP that’re if not specific, then at least detrimental to performance in the UK. Average humidity is high, which is why we get wet snow and ice formation more than other parts of Europe. The humidity can affect the performance of ASHP as the temperature approaches zero requiring substantial input energy for defrost cycles.

I want ASHP to work, but in reality, for it to be carbon neutral at the local level, I’d need to double the size of my solar array (input energy) for the winter, somehow install external insulation onto a wall subject to driving rain and high winds, rip up every floor and insulate and replumb, install a 210l unvented tank and electronics for solar thermal, install therma skirt or MUCH larger radiators upstairs and UF heating downstairs.

The price will be close to £35-40k, but I’d also need to find people to do it. It took me almost a year to find a solar guy and a roofer who’d work together on an in-roof solar and re-roof.

Quick question – why ASHP, and not electric radiators?

Quick question – why ASHP, and not electric radiators?

Electric rads 1 unit in = 1 unit out – all of the time .

Ashp has potential for 1 in 3 out some of the time remembering it works on the kelvin scale so as pointed out above there’s always “heat” in the air ….. But around here they still plummet to 1:1 in winter

Flip side is – 22grand buys a lot of radiators and electric.

My old man’s was installed courtesy of the  gov due to them being in hospitality. It was not 22grand. It’s more expensive than the oil it replaced

Boreholes for vertical GSHPs are normally waaaaay deeper than that, 100m is more likely.
</blockquote

Was gonna say this, my parents have just had three 230m bores sunk for their gshp install. It’s feeding a 25 year old, very well insulated 460m^2 house in northern Donegal to replace what looked like a small steam tugboat boiler.

Their heat store is amusing

Do you happen to know and could you disclose what they paid for those holes?

OP have you checked out https://protonsforbreakfast.wordpress.com

I’m expecting we’ll make a change to an ASHP sometime soon. I do not expect to save any money in running an ASHP. I do expect to eliminate our dependency on gas.

GSHP would be an interesting, yet expensive, option if we were in an empty area with land. Not an option with a mature garden and city-edge living.

When considering the future, I assume it’s a given that oil and gas will continue to get more expensive (as a general trend) and for alternatives to work electricity needs to get cheaper (relatively)?

Also burning any alternative hydrocarbons is surely only a interim solution?

ASHP will be better than 1:1 in winter, or should be with the correct design.
As someone has said it is the humidity at low temp that kills the efficiency compared to scadanvian countries

Heatgeek on YouTube is worth a watch about gshp and ashp along with other alternatives.

https://youtube.com/@HeatGeek

My sister just had ASHP installed for free via a grant. There’s no gas in the village and the 90s house didn’t have any central heating, relying on a wood burning stove and storage heaters which were of course crap. The new radiators are huge as are the pipes, so let’s hope the insulation is good enough.

My in laws got a brand new GSHP a couple of years ago. One borehole, i *think* 12cm dia and 120m deep. That replaced a pellet burner (with electric boost on the tank), which in turn replaced an oil burner that had been in since jesus was a young man. It’s about 120sqm house, built in the 1880s and insulated with wool and straw with asbestos cladding… It leaks like a sieve. They paid a little over 25k (about 2/3rds for the drilling), heating bills are less than half now. And FiL doesn’t have to clean the burner out and empty the ash tray anymore.

Mine is a 130mx15cm borehole (i’ve got the original receipt), that heats my well insulated 200sqm house (triple glazed, 300mm insulation in the attic, heat reclamation system in the attic) “adequately”. It needs a bit of a top up when it gets below about -10 outside. It was installed in 2001, so the price is irrelevant! Biggest issue is the radiators weren’t replaced, so it’s still got the small ones designed for high temperatures.

Also, we’ve got 4 or 5 local companies that are bidding for drilling/installation work. Whereas you guys in the UK will have a much more limited list i guess!

BTW This is in sweden, where minimum standards for insulation are a lot higher and GSHP/ASHP has been mainstream for years.

Fitting larger rads is easy though, if you have the space. I’ve done one, I’ll do a couple more this winter.

Large rads is easy, but large pipe work isn’t.

Easy but expensive, i’ve got 14 of them still to do.

Boreholes were £10240.

Drilling rig was amusingly small. 

This is something I do know about.

Ground vs Air. Ground costs a fortune to fit, around £10k extra for the boreholes. Then there is the problem that the heat from the ground is sucked out, and not replaced quick enough. It has been known for the ground around the bore to freeze, as the heat transfer undergound just isnt fast enough to replenish the heat taken by the pipes.

ASHP benefit in the Uk from an air tempertaure that doesnt go below 5 degree c for something like 90% of the time. (OK, the Cairngorms get more cold days, but in general, over the UK,the air stays above freezing for most of the time, and above 5 degrees for 90%+). The COP in Summer months for heating the water can be as high as 6, the ground source will still be at 10 degrees in July, so a COP of 3+ could be expected.

Insulation/older houses and other fallacies. It is untrue. A HP can be fitted in any premises,and should be roughly equivalent in running costs to a gas boiler (obviously gas and electric prices differentials affect this, but it has stayed typically a price of 3:1 for a while now). The COP should be 3 or more. More will make it cheaper to run than a gas boiler, and certainly cheaper than an oil boiler. Insulation, of course insulation helps. It helps whatever heat source you have. If your heat loss from the house is 10kW, it’ll be 10kW whether its gas, oil or electric that heats it.

Larger radiators and piping is required. Not always. My CH is 30+ years old. I tried it last year by running the gas boiler at a flow temperature of 35 degrees. It was toasty as ever, and in running at the low temperature, it made my gas boiler more efficient, as it wasnt cycling as much, and condensing at all times it ran. A HP would be a straight fit in, I have standard single panel rads and 15mm pipework in a 3 bed semi. No change in eithe ris required.

Install cost is the killer, though, it is coming down. A straight swap of a gas boiler can be done for less than £2k, a HP will be likely £6k+ There are some right cowboys out there now fitting them, mainly as the Govt. put up the £5k subsidy, but I doubt the householder will see much of that, the installers are taking the bulk, by increasing their install charges. This has been complained about a lot in the Trade, as to claim the £5k you need to be MCS registered, and it is not easy, cheap or quick, for a Sole Trader to achieve the MCS registration, thats why larger Companies are promoting themsleves so much, sending out Fitters who have not had the relevant training, and the HP is never going to be running properly or at its most economical.

The Industry are aware of this, and MCS are consulting now to reduce the burden in being a Member of their scheme. There are 3rd Party Companies who will apply for the MCS for you, but the typical cost is £1800+, just for them to process the paperwork, adn claim the £5k.

Oil boilers, IIRC, they are not allowed to be fitted new (or replacement) after the end of this year. Yes, thats right, so if you want a new one, get on it quick, or you’ll never get a new one fitted.

Boreholes were £10240.

Drilling rig was amusingly small.

Generally a geotechnical unit .

My neighbour hit granite cap and had to go to 300m. The unit they had to bring in cost more on hire than the original total install cost …..

Thanks for all the replies.

To answer a couple of queries:

No microbore pipes in the house (one of the things I checked before buying), so the larger rads are all that would be needed upstairs and are already included in the quote I’ve had.

Air source over ground source is indeed a cost thing, I’ve had a quote I consider reasonable for the solar plus air source and all required upgraded rads/hot water tank.

im not too worried about the installation cost, but I’m very interested in how much it’ll end up costing to run… I can swallow the up front costs, but not if it’ll double my heating bills going forward!

@alanl that was really insightful, thank you. Reading this wondering what we will do (oil, mid 2000’s stone built house).   Oil boilers not being available post 2023 is a bit scary. Albeit we replaced ours 18 months ago. So should have some time.

Oil boilers not being available post 2023 is a bit scary

Good job it’s not true! I’ve been following this closely and have seen nothing of the sort. There was a consultation but no decision as far as I can tell. The earliest was like 2025 in any event.