Air source heat pump or alternatives to Gas

I know some of this has been touched upon in other threads but not seen one dedicated.

We installed Solar at the start of Nov with a home battery. Our Gas fired heating system also needs replacing as it is very old (40+ yrs) but works ok. The solar has been more effective than I thought it would be and my original plan was to replace the heating system with the same, keeping our immersion tank (actually replacing with bigger as the PV powered iBoost is actually quite effective even in Nov/Dec) I expected both projects to be separate and although I only have a small amount of data to work with, the PV has been surprisingly effective even over this short winter period. Given the very high price of replacing our heating “like for like” due to other upgrades that need to be done it got me thinking about how realistic it is to replace our heating with electricity (we have another lower roof which could hold an additional est 5kW of PV) or install an ASHP (something I had not considered due to cost and the possible need to replace a lot of our old radiators and piping)

What are the alternative heating options and STW experiences of replacing with electric/Solar etc

You can’t rely on solar pv generating enough power in winter to run electric heating even in a really well insulated house. Passive house plus, which is pretty much the gold standard, still normally models buying in power over the winter at cheap night time rates and using battery storage. Justin Bere architect has some good case studies on this on his web site. I have generated far more than normal winters over the past month due to a lot of clear bright days. All electric is a good idea, just do t think you can heat your house for free. Also make sure building fabric is up to scratch. There is a 5k grant for ashp installs

an ex colleague writes a blog about things scientific, including his journey towards being ‘off grid’ for heating and electricity which might give you some ideas how achievable it is.

In a recent one or two he’s also given a couple of lectures and I think his slide deck and maybe even a recording of it is linked.

My House

an ex colleague writes a blog about things scientific

That looks really interesting thanks!

All electric is a good idea, just do t think you can heat your house for free

Not cost free but free of Gas. I have a home battery so being proactive in its use during the day is very interesting, I charge it on eco7 overnight. Fortunate that I can do this in terms of making use of spare solar when the battery is full and any spare would be sent to the grid at a low cost.

Why do you want to get off the gas network?

For me not knowing your exact circumstances or house
1. Get an unvented cylinder with a ASHP coil and at least one immersion heater fed off the PV batteries to maximise the use of this.
2. Sort your insulation out as best you can. Future might mean lining walls with insulation board when redecorating.
3. Refit pipes and radiators to suit the lower temperatures of an ASHP type system
Then depends if an ASHP is sensible at this point for your house.
4. Fit an ASHP if you it’s suitable or get new gas boiler in a configuration that you could add an ASHP onto the system alongside it.
Both then give you the option to run the ASHP spring/Autumn and then gas over peak winter when the ASHP is inefficient. You may not get the grant if you keep a gas boiler though.
You could control it automatically to switch between the 2 but manually switching between the 2 is probably easier.
Remember the ASHP will use your PV but there probably won’t be enough in winter to do much. You could make it empty the batteries on a morning and get what heat you can for free into the system then switch to the gas boiler.
The other problem with ASHP and other green tech it tends to need space to fit it. I’m lucky my loft is ridiculous but currently still only running off a gas boiler. While I have a spot for an ASHP I haven’t put the pipework and rads in to suit it. My thought back then was an ASHP will work on smaller pipework and rads but it won’t heat the house mid winter fully. The rest of the year it’ll manage.

We moved to a 4 bed new build with no gas just over a year ago so ashp and everything else is electric. Well insulated but nothing like passivhaus.

Rads are double panel convector but not huge.
Pipes at rads are 15mm. Some of the central runs are in 22mm. Only the feed to / from the ashp is (I think) 28mm.

Some very rough consumption numbers if they might be useful:
Total 1st year electric consumption for everything is 6700kWh. That is for comfortably warm all the time during heating season (one person WFH) and running long low and slow as not efficient or effective constantly turning on and off. Having seen some of the gas and electric consumption figures in other threads I’m pretty happy with that.

That consumption also includes most meals cooked at home and about 2-3 hours a week tumble dryer in winter. Late teen kids so a chunk of washing when they are home. Average of at least 3 people at home over the year.

Probably also running things a bit hotter than we would have liked for the first 3 months whilst getting controls right and drying out.

The week just gone is probably a good absolute worst case with 8 freezing days getting down to -11C outside some nights. Averaged something like 31kWh a day. And it never missed a beat or failed to keep us warm.

PV on the south facing part of the roof will be a next step sometime (shame building regs didn’t force the developer to do that).

Why do you want to get off the gas network?

A few reasons. I would like to reduce my use of fossil fuels and my gas boiler needs replacing very soon so now seems like a good opportunity to explore alternatives. I had solar installed recently which has opened my eyes to harnessing more electricity and using it as alternative or the possibility of installing an ASHP.

Thanks @tomlevell really interesting. 4 bed detached so is space for an ASHP but it would mean basically re-plumbing the entire house as we are on 10mm piping. A significant job and a great deal of disruption which would make me very unpopular….
The house does have reasonable insulation, Double glazing, cavity wall insulation and a very well insulated loft. Interior wall insulation may be something to investigate.

Really interesting @mick_r thanks

I only know one person with an ASHP and he says it’s crap 😀 I guess in a very well insulated house specifically designed for it, it makes sense. But not so much as a retro-fit, maybe. Although, being able to use solar PV & cheap rate electricity with a battery to bring heating costs down, might be able to tolerate a bit of crapness 🤔 Plus reducing reliance on gas is a good thing for several reasons, I think.

I know loads of people with ASHP and/or GSHP.
No one seems to complain about either of them. But the houses are (generally) built for that sort of heating. Or the systems they install are engineered to account for the building.

We have AHSPs in the air handling units at work along with heat recovery wheels and LTHW radiators. At extremes of operating temperature range they are shite. Air too cold the unit ices up and blows clod air turning the room into an ice box, air to hot and the unit flops the other way and blows hot turning the room into a sauna.
Out of 5 ASHPs 4 failed last week, meaning we could heat the rooms or ventilate the rooms but not both.

The system or relatively new and designed by M&E consultants as part of a £12M building refurbishment.
We are based in Fife.

Of the two people I know with ASHP, both have been struggling this last week with the very cold temps in the SE, endlessly de-icing and not doing much heating. Admittedly we only get temps this low once every 10 years…

Can you run your gas boiler at a much lower flow temp to see if it actually heats the house still? This will go some way in imitating an ashp setup. If the house struggles to hold the heat then ashp will not work for you. Definitely try and time it when it’s really cold outside.

That should be ashp wont work for you without increasing the size of at least some rads. But yes you can gradually turn down flow temp to around 50 and see if it works ok. Obviously with longer run times. All those with ashp that don’t work when it’s cold didn’t have them designed and sized appropriately for the building heat loss, exactly the same as fitting a too small gas boiler.

Sorry ajc, you are right in terms of size of heating item. I hardly know anything about ashp in terms of sizing and setup for poorly insulated houses.

Whilst reduced reliance on gas is worthwhile it’s worth being aware that for the foreseeable future, during most times of heating demand, the extra electricity demand from turning on an ASHP will be met by additional load on gas and coal power plants.

If you need to replace the radiators and piping in the house then those components are carbon intensive to produce. I looked at it for our place and can’t see how adding extra load to the grid, which is already straining, is a responsible thing to do. Hopefully in a decade or so there will be more renewables and wind so the carbon sums will add up.

Whilst reduced reliance on gas is worthwhile it’s worth being aware that for the foreseeable future, during most times of heating demand, the extra electricity demand from turning on an ASHP will be met by additional load on gas and coal power plants.

Does the efficiency of ASHP overcome this though? I’m sure I read somewhere that even if you make the electricity 100% from coal it’s still less C02 intensive to run ASHP than a gas boiler. This may have been in some marketing material though, so I’m not entirely convinced.

If you need to replace the radiators and piping in the house then those components are carbon intensive to produce.

Would love to understand the numbers on this better. Does retrofit become more carbon-costly?

What is the noise from an ASHP like?

Whilst reduced reliance on gas is worthwhile it’s worth being aware that for the foreseeable future, during most times of heating demand, the extra electricity demand from turning on an ASHP will be met by additional load on gas and coal power plants.

Gas boiler is 90% ish efficient whereas a heat pump, even during the week we’ve just had, has a coefficient of performance (COP) of 3 or 300% efficiency so will require three times less gas, or coal.

ASHP to gas running cost wise will be similar, although if you have well designed system and can use you heating effectively it will be a little bit cheaper. Not enough to warrant doing it just to get rid of a gas boiler, however if your gas boiler is at the end of its life and you are replacing it then cost wise it starts to make a bit of sense.
If you are wanting to replace rads etc anyway then even more so.
You may qualify for the £5000 grant and also any work associated with the installation ie the rads etc will be zero rated for VAT at the moment. You may be able to use some of your mini bore pipework, unlikely but it can be ok for some radiators, it would be best to change it though.
Choose your installer wisely, design is critical, stay away from Daikin, look for a unit that uses R290 as a refrigerant.
If you’ve got solar panels already consider putting in a big buffer store if you have space. Then you can heat it when you are generating and utilise later. You might also have a cheap overnight tariff which you could use to load the buffer. The marginal gains way of running a heating system!

Can I ask why ASHP’s are not often installed under a small roof area, possibly even sides on? It seems in the snow and ice, or indeed extreme heat, siting the unit in some shelter would be a Good Thing.

In fact, would it make sense to sit an ASHP at top of a Trombe wall, a greenhouse or even inside a garage or similar?

Whilst heat pumps achieve greater than 100% efficiency generating electricity from fossils fuels is inefficient. An open cycle gas plant or a coal plant is generally about one third efficient. So by the time you account for 5-10% transmission losses a heat pump with CoP of three would end up similar efficiency in converting fossil fuel to heat as a good gas boiler.

I believe most gas in the UK is burned in more efficient combined cycle plants. However, I understand these are generally being used as baseload  these days in the UK. So if I turned on an ASHP the additional demand from the grid wouldn’t be met by such an efficient plant. But thinking about these numbers does make you think that building new efficient gas plants could be a useful contribution to decarbonising heating in the UK.

What is the noise from an ASHP like?

Noticeable but not intrusive. You probably wouldn’t want one outside your bedroom window, though. My neighbour has one and it sounds a little bit like a fridge motor, so more of a hum / low frequency vibration than any particular sound of air noise.

Compared to an oil boiler flue it’s virtually silent though.

In fact, would it make sense to sit an ASHP at top of a Trombe wall, a greenhouse or even inside a garage or similar?

No. It needs a good flow of air to be sucked in, that air is compressed, and comes out at roughly 10 degrees colder (obviously depending on ambient temperature), that air expelled will act like a fridge, and the small area you are sucking air from will soon be 10 degrees colder than ambient.Maybe possible to put the inlet in a sheltered place, and make the exhaust vented outside, but, all manufacturers advise against it.

Morning all,
TLDR,
Heat pumps work in cold temperatures and IMHO have advantages over gas going forward.
If replacing an old gas system as in the OP then ASHP should be considered.

I had an ASHP installed in my home just over two years ago replacing gas.
The house is 2013 build 4 bedroom in Scotland, well insulated but nothing special.
ASHP is installed against a north facing wall, never sees sunlight in winter.

The ASHP has kept us warm through a long cold spell in 20/21 and the last cold week.
If an ASHP is not operating correctly in low temperatures then there is something that needs to be check for that installation.
Please do not believe those who tell you that ASHP does not work in the cold, they just do.

My normal winter daily electricity use is low 20s kwh normally, can be up to 30 kwh on a very cold day.
That is all heating, cooking, lighting etc and two people in the house all day so kept warm.

We had small diameter ‘microbore’ heating pipes for the gas system, all of that needed to be replaced so it was a big installation. Larger radiators also but not obtrusive.

Regarding the point of burning additional gas at peak times, yes but no.
ASHP will use about 1kwh of electricity to produce 3kwh of heat, you therefore burn less gas per kwh of useful heat.
In the future the % of fossil fuels will reduce so the advantage will increase.
I personally see electrification as the way forward as it allows for better control and diverse sources of generation.

As mentioned in another thread, if you’re installing a HP, give a thought to who is going to service and repair it. We have a problem with ours just now and nobody wants to know as they’re busy installing new systems. I suppose eventually that will be resolved, but until we get visas sorted for Polish heating engineers to come back and help us, it’ll be pretty cold.

(I think this may be the case for electric cars also?)

So if I turned on an ASHP the additional demand from the grid wouldn’t be met by such an efficient plant. But thinking about these numbers does make you think that building new efficient gas plants could be a useful contribution to decarbonising heating in the UK.

Yes gas fired peaker plants are not combined cycle but ASHPs are not like switching millions of kettles on or everyone cooking dinner at the same time they will be base load and taken care of by combined circuit gas plants, nuclear and wind. Building new fossil burning plants is not any kind of answer especially as they are not replacing coal plants these days. We need more wind and massive grid scale storage.

The problem is that wind and storage doesn’t exist in the medium term. We are already stretched for generating capacity; coal plants have been running all year. Additional load on the grid won’t be met by efficient generation in winter for a good five years, it will be met by coal, OCGT and at the worst times diesel generation. It would be great if that wasn’t the case, but it is.

Thankfully lockdown got me aquainted with Technology Connections on YouTube. This gives some really useful info on many things, heat pumps included. Before considering heating alterations, I’d watch this set of vids…

and for info re gshp, this one…

Granted they are a bit long winded, I’ve tried to order them in relevance to this thread.

On the heat pumps use electricity thing…

A gas boiler is around 96% efficient.

CCGT is around 50-65% efficient – lets say 50%. Allow say 7% for transportation losses and that’s 46% at the house.
ASHP has a gain of 2-3 between the energy in and out – lets say 2.
So about 92% efficient use of gas as opposed to 96% in the boiler.

And it’s not so good in the coldest weather.

But GSHP has a gain of 4-6 and does work in the cold.
So even running off a CCGT, GSHP is better than a boiler.
And there will be some wind or nuclear or solar most of the time.
But they aren’t cheap to install – at present.

Correct my figures if I got that wrong.

Experience with Air Source Heat Pump

The quoted ASHP quoted figures sound reasonable, however the comment that GSHP work in the cold has potential to mislead.
I have used an ASHP for two years in cold weather and can assure people that they work.
The frequent statements that ASHP do not work in cold weather are not helpful.
Norway and Sweden have higher % ASHP than UK.
Rant over 😉

The problem is that wind and storage doesn’t exist in the medium term. We are already stretched for generating capacity; coal plants have been running all year. Additional load on the grid won’t be met by efficient generation in winter for a good five years, it will be met by coal, OCGT and at the worst times diesel generation. It would be great if that wasn’t the case, but it is.

None of this is an excuse not to switch to heat pumps, or EVs come to that, because as we decarbonise the grid every heat pump becomes cleaner. The emissions of a gas boiler are baked in when its made.

Got a NIBE ASHP for my 18-month old house on Isle of Mull – house is pretty well insulated, 110m2 and electricity bill is £180/month, plus I get £600/yr RHI payments. There’s no mains gas here.

My priority would be to look at insulation and air-tightness first. Also, windows and doors as these have improved a lot in comparison to badly-installed, cheap UPVC ones.

Lots of problems with ASHPs is down to poor specification and installation in a badly insulated house.

Can you run your gas boiler at a much lower flow temp to see if it actually heats the house still?

I have been doing this in the recent cold spell, and have the flow temperature down to 45ºC with 0ºC outside, and maintaining the house at 18ºC. I think that’s encouraging for the prospect of ASHP. My boiler is only 2 years old so I don’t plan to install ASHP any time soon, but it’s useful to have an idea about whether radiators will need replacing as it’s something to bear in mind when redecorating.

Dovebiker – any idea what you are using in kWh? You probably have the most insulated house so would be good to compare (my numbers look similar to littledaves).

And as for the icing up comments – I’m totally unaware as to how often ours has done a defrost over the last sub zero week. It isn’t running it’s nuts off and we have never been lacking in warmth. It just works. People either spec them wrongly or drive them wrongly.

After 25 years with the convenience of gas combis I thought we would really struggle with ashp and a water cylinder, but I’ve been pleasantly surprised. They are also surely a prime candidate for smart grid control that knocks them off for short periods of high demand and maximises use at quieter times.

Our entire estate has them and noise is minimal. They do seem more intrusive on the older terraced estate next door where they are right by your back door / neighbour.

Gas boiler is 90% ish efficient whereas a heat pump, even during the week we’ve just had, has a coefficient of performance (COP) of 3 or 300% efficiency so will require three times less gas, or coal.

No chance it’ll be running much closer to 1:1 as it needs some warmth in the air to do it’s black magic.
Overall they tend to quote 3.5:1 for the entire year.
They certainly work mid winter but not exactly efficient.

One thing to keep in mind with just reducing gas boiler temperature is that you still need bigger pipework for the ASHP as it runs at a lower temperature differential to achieve the same output.

An ASHP doesn’t need the air to be warm to work. An ASHP will work down to about -20, it just needs energy in the collector, in the case of ASHP that it the air around it.

It will be better than 1:1 otherwise they wouldn’t be able to produce a greater output than input.