@cookie197 - welcome to the forum. There is a wealth of knowledge here and I am confident others will chip in soon but I can say something about running costs based on my own experience of changing from oil CH to an ASHP. My experience is not universal, others have done much better, but I did not see any savings. 

There are two costs to consider: costs in kWh (actual energy) and costs in £££. A system might cost the same in energy use (same number of kWh) as another but if the fuel used costs twice as much per kWh, then that system will cost twice as much to run. At the moment, cost per kWh for electricity is a lot more than it is for oil (and indeed a free supply of wood for burning). According to boilerjuice, CH oil is currently about 75p per litre, and as there are roughly 10kWh of energy in a litre, that is (very roughly) 7.5p per kWh. Electricity is whatever you are currently paying for it.

Thus, if your proposed heat pump used the same amount of energy, then your costs would go through the roof. However, heat pumps are much more efficient than even the best fossil fuel boiler. Whereas 1 kWh of energy into a fossil fuel boiler might give you back 0.8kWh of heat energy - 80% efficiency, a well installed and run (nota bene the tales of woe through the forum) heat pump might, for each kWh put in, give you back 3.5kWh of heat - 350% efficiency (and also a COP (coefficient of performance) of 3.5, which is another and common in the heat pump world way of expressing efficiency).

If we say (to keep things simple) that a heat pump is four time more efficient that a fossil fuel boiler, then the break even point - the point where they both cost the same in £££ to run - is when electricity is four times the cost of oil. The fossil fuel boiler needs four times as much energy put in to get the same energy out, but the fuel is a quarter the cost - so it cancels out and costs the same in £££.

So far so good, but there is another important factor which applied to me, and may well apply to you, which isn't widely appreciated. Fairly soon, if you haven't already done so, you will pick up the idea that heat pumps are best run 24/7, with actual output determined by the leaving water temp (LWT, the temp of the water leaving the heat pump), with that usually determined by the outside ambient temp. The colder it is outside, the higher the LWT. The reason for running the system 24/7 is that by and large heat pumps are rather feeble beats. Unlike fossil fuel boilers, which can put out ferocious amounts of heat, and heat a house very quickly, heat pumps behave more like steady Eddy, and need as it were to keep up their momentum. If they slow down, they take a long time to recover. The idea with a heat pump is that you put just enough energy into the house all the time to keep it at design temp, so it never has to do a recovery from colder temps.

Crucially, if in the past the householder had run the fossil fuel boiler on a time (as I did, say six hours in the morning and six hours in the evening), then the heat pump will run to a very different pattern, being on 24/7, meaning the householder doesn't get any savings from heating off periods, when the house does get a bit colder, but it doesn't matter, because the occupant are either in bed or out and about. The house will be warm all the time, whether it needs to be or not, but as a result the energy demand will increase dramatically, in my case by a factor of about two (it is difficult to quantify exactly, because so many variables change, meaning that is just a ball park figure for changing from timed heating to 24/7 heating).

The bottom line is that moving from a cheap energy source (oil) and the change from timed to 24/7 heating means that I am certainly not saving money by having a heat pump. Again, there are a lot of complicated variables at play, not least the volatile prices for energy, so again it is hard to compare like with like. On the other hand, on the positive side, I have a 'green' heating system, no need to check levels and order oil, a bit more space in the house as the heat pump is outside, and perhaps the best thing from a comfort point of view, no condensation (which use to happen when the house cooled down at night, which it no longer does) and a house that feels dry.

If I knew all this when I made the decision to go for a heat pump (which I didn't), would I still have gone for one? Yes, but with even more trepidation than I had without knowing this! 

I think there are a couple of important factors to add to cathodeRay's assessment. Since your house is well insulated, your heat losses will be low and you wont lose a lot of heat overnight (or day) if you choose to run the heat pump 24/7. I dont run mine like that, in my last very well insulated home, I had two 'on' periods in the morning and afternoon and my bills were peanuts. Insulation is a KEY factor in making a heat pump work well.

This brings me to my second point, which is if you have solar panels you are essentially getting your electricity for free for a good portion of days in the year. You dont say how much PV you might get, but clearly the more the better! If you are producing a lot more than you are using in the day, then a battery does make good sense and it can also be used to store cheap electricity from a TOU tariff like Octopus Cosy, when there isnt much winter sun around.

Having a wood burner is also a nice extra, as on very cold days, when the HP might be expensive to run, you can just boost things a bit.

My experience, using a heat store with a heat pump gave me lots of hot water, so i wouldnt even consider that an issue. In hindsight and with my new house, I have a pressurised cylinder (Mixergy) which is a better fit than a heat store for a heat pump. Although Im not actually using my HP to create hot water at the moment, Im just using a solar diverter and immersion heater. I will monitor it over the winter to see how I want to go forward with that.

My own personnal experience is that a HP is cheaper to run than a gas boiler and if you are getting the work done for free then it would be a no brainer. That said many of us on here are not doing it for purely financial reward. There is also the possibility that this kind of financial assistance wont be around forever.

You really have to average the costs of the heat pump to run over the whole year and not get fixated on winter bills which some people do. There are also lower service costs to consider (my last HP ran for 11 years, until I left without ever being serviced, just me checking the antifreeze level and clearing the occasional leaf) they really are very low maintance.

BTW where in West Wales are you?

@cookie19

My pump, replacing an ageing but still serviceable gas boiler, is due to be installed w/c Oct 16th after a journey of about 2 years. With that caution... my personal advice (which I would now give to anyone) would be:

If you can afford and are willing to take the time to learn about the technology and your house in relation to the technology, then do so.  It might take a year or two and you might have to speak to several installers as well as getting help from this forum and elsewhere.  During the process you will as a minimum work out easy routes for services/best place to locate things.  More importantly - there are good installers out there, but also quite a large number who will quote an overpriced, over complicated system which will cost you more than you need to pay, will involve lots more disruption than is necessary, and ultimately is less likely to be satisfactory.  I call these people grant harvesters, they have a flashy website and a swish salesman,  and will do 'installation by numbers' for an inflated price.  They are of course all MCS certified, but that doesn't appear to guarantee quality.  Doubtless the grant harvesters will go out of business once the grants dry up and the industry matures, but it may be a few years yet.  Being an intelligent customer should give you a better chance to weed out the cowboys, and get a good system which meets your needs not the needs of the installer.

I would make an exception to this if your house fits the 'profile' that the 'big boys' (eg Octopus) are currently fitting to.  They seem to be doing a reasonable-good job from what I have heard (which is not much, but all positive) however they are clearly cherry picking a particular class of job.

If you cant wait, or the grant is time limited, then either seek recommendations, or run quotes past this forum (and any other forums you have joined) to get commentary.  This should weed out the cowboys without necessarily having to understand it all yourself.  Along the way you will probably go through an accelerated learning process anyway.

BTW it pains me to have to say the above, I am passionate about tackling climate change, but the experience of the past 2 years, and listening to others on this forum and elsewhere, has sadly re-emphasised that 'caveat emptor' holds firm.  Its not the technology itself that's the problem (although there are some further developments that would help), its the immaturity of the UK installation industry.  I should add that I am in the South east of England, in Wales the situation may be better.

Obviously I cant comment with any authority on relative running costs and in any case, over the life of the unit, the relationship will change.  Energy prices are largely a function of either global or local politics so today's cheap fuel could easily become tomorrow's expensive fuel.  I'm designing/aiming for (and will be satisfied with) price parity with gas.  As I have solar PV I may well do a bit better since shoulder season heating may be at least in part free (and summertime cooling, on the few days its worthwhile, will definitely be free).

I hope that helps.

@jamespa 

Thank you - that's very interesting. I suspect that the people who are trying to get me to sign up are exactly the sort of "installers-by-numbers" that you refer to. I imagine that they have a set kit that they install everywhere, without taking into consideration any other factors. I just don't want to end up with a system that isn't fit for purpose because I've been bounced into making a decision. There is quite a lot of pressure along the lines of "the grants won't last for ever, so you need to be quick", etc. I think you're right - I need to sit back and learn much much more about it, so that at the very least I can brush aside the "cowboys", for want of a better word, and install the right system for our property, even if it is a couple of years down the line. Thank you for taking the time to reply - it's much appreciated.

@cathoderay 

Thank you for this, and for your brilliantly simple explanation of the figures, which I actually understood! I visualise the difference between the oil boiler and the heat pump as the hare and the tortoise, and I can see why the HP will take ages to rewarm the house once it has cooled. It still feels oddly wrong to run a heating system all the time, since for years we've set ours only to come on when the temperature drops, rather than on a timer for set hours. Not having to mop up condensation every morning would be a boon as well, and something I hadn't thought about! Thank you for taking the time to reply - it's much appreciated.

@bontwoody 

Hi - thanks for your comments - I was quite worried about the hot water, but it's clear from what you say that it's not as big a problem as I thought. When I asked the surveyor he was a bit cagey, which made me suspicious, and he muttered about putting in a standard hot water cylinder as we don't currently have one. He also couldn't or wouldn't tell me exactly which make/model/size HP would be installed, nor how many solar panels etc - he said it would depend on the company's calculations, which may very well be true, but leaves me a bit in limbo. My understanding is that based on his survey, the company will put together a package and then send me the details, so at that point I'll have a much better idea of what to expect. Btw, you're the first person who's told me that the HP doesn't have to run 24/7! I think I've said elsewhere that it feels "wrong" to run a heating system when it doesn't seem necessary, but I think I just need to learn a new way of thinking about heating. And I'm with you on tackling climate change, and going over to green energy, but I don't want to make a huge mistake by rushing into installing a system that seems to have so many detractors ... Another issue for us is that we may move house in a couple of years when my daughter leaves uni, and I can't work out whether having a HP system installed will help or hinder that - but that's another thing altogether!

We're near Llandeilo, in Carmarthenshire. Beautiful area, and a relatively mild climate, as we're protected somewhat by the "Pembrokeshire Dangler" - even the Beast from the East didn't bring us any snow, though it fell to east and west of us!

Thank you for taking the time to reply - it's much appreciated.

@cookie197

Hi Cookie, welcome to the forum.

It would be interesting to know about the grant system in Wales in comparison to the £5000 grant now being offered in England towards heat pump installation.

I would not feel confident, one way or other, in advising anyone to get or not get a heat pump installed during the present energy crisis. I am quite happy to help those who have taken the plunge to hopefully get the best performance from their system.

I would certainly recommend having a solar PV system installed, and in your case to also include a battery storage system. Since you have a combi type boiler I am assuming that you do not have a hot water cylinder, which would limit how much of the available output from the solar PV could be utilised within your home. I think that the average daily electricity consumption is in the 8kWh to 10kWh per household, so with even a modest solar PV array and battery storage system this figure can best greatly reduced for much of the year. Since installing our own 4kWp solar PV system over 10 years ago, it has reduced our electricity import by 50%.

I suspect that having solar PV and a battery system would also add value to your home.

But rather than just take my word, monitor how much electricity is used daily over a period of time, then assess what size solar PV and battery storage may be required and how that fits in with any grants available.

Posted by: @cookie197

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It still feels oddly wrong to run a heating system all the time

Indeed it does, and it is counterintuitive. If we imagine heating a house to be like keeping a bath with a leaky plug hole full, then it stands to reason that keeping the bath constantly full takes more water than letting the level drop for a while, until we realise that bringing the level up to the top again takes more water than just keeping up with the leak. This is the complicating factor: how much extra water/energy is needed to raise the level/temp, over and above that needed to maintain the level/temp. I should add that I suspect this analogy is not ideal, since I am pretty sure the recovery period (getting back up to level) will use exactly the same amont of water as keeping it at top level all the time - unless, perhaps, the higher hydrostatic pressure from being full means the rate of loss is higher when the bath is fuller (and it is just possible the same applies to heat energy, when the temp is higher, the rate of loss is greater).  

I have never managed to get to the bottom of this question, though I do have some thoughts, One key factor has to be the length of the setback period (setback being the somewhat obscure term for the period when the heating is off - presumably derived from idea that the heating has had its thermostat dialed down, ie setback, when in reality it is a timer that has turned the heating off). Given a long off period - say a week - then clearly one saves energy. But what happens over shorter periods, say over night for six hours? Clearly one saves six hours worth of energy use, but that has to be set against the extra output needed during the recovery period. On balance, I am still pretty sure that the laws of thermodynamics mean that it must take more energy to keep an entity, in this case a home, at say 20 degrees all the time, than to keep it at 20 degrees for 12 hours a day, and allow the temp to fall a bit in the other 12 hours, but I am stumped to give a mathematical proof for this.

But in reality, we are overtaken by the characteristics of a heat pump, and its inability to run really fast and furious. It has to by and large rely on 'heat momentum' to keep on top of things, hence the general advice to keep them running 24/7. On normal settings, my heat pump takes hours if not days to recover from a setback, be it a deliberate one set by me, or an external event, like a power cut. Here's a chart of my kitchen room temp during a trial period of setback last December (on this occasion, this was a setback, from 19 to 16 degrees, rather than a binary on/off, though in effect it behaved as if it was a binary on/off, ie the heat pump didn't run at all during the set back period). As you can see, it took all day to recover from the setback. In fact it only really got back to design temp in time for the next setback, had I not turned the setback off:      

That said, there is an option to boost a heat pump's output, usually by increasing the LWT. I believe Ecodan's have this built in, it is called something like auto-adaption, and it is possible that Homely, a 'smart' control system' also does it. But asking a heat pump to work harder is a bit like asking an asthmatic to run faster, it tends not to work very well. And with heat pumps, there is a built in penalty: as LWT goes up, efficiency goes down, meaning any post setback boost will cost more than steady running over the recovery period. Nonetheless, I have been toying with the idea of testing overnight setbacks with a post setback LWT boost this coming winter. Midea heat pumps (which is what I have) have a fairly accessible interface that one can connect to using a computer (covered in posts elsewhere on the forum) and the computer can then be used both to monitor the heat pump and, in theory, control it, though I have yet to try this. I worry it might turn out a bit like lowering the rods into a nuclear reactor, with no way of pulling them out again...      

@cookie197 

Morning, You will need a hot water tank, but be careful about the 'standard' variety. HPs need a bigger heating coil or a heat exchanger for the cylinder. I can thoroughly recommend Mixergy but they arent cheap, however Im hoping to be able to offset the extra cost by heating less hot water (see the info on Mixergy out on the web).

A major issue for you would be whether you move or not in the short term, however if it is paid for then its just the inconvenience of fitting you have to worry about. Myself I would say the fitting of the HP and solar panels would be an asset on sale but you could ask a local estate agent.

As others have mentioned I would definitely get a quote from Octopus. They know what they are doing and it will give you a ball park to work from. Your house sounds like the type of 'low hanging fruit' they are looking for. 🙂 After that maybe have a look for heatgeek certified installers (search for heatgeek on youtube)

With respect to running 24/7, it does depend a lot on insulation and underfloor heating helps a lot too as you have a slow release of heat from the slab. Walls can work the same way however if they have good cavity or external insulation. HPs are definitley more efficient run 24/7 but if you are producing free electricity from solar panels then just take the effiency hit and heat your home when you have the free stuff!

Have a look at my blog (link below) to see what I have done. I live in Pembrokeshire now but moved from Swansea so know Llandeilo well. If you wanted to come down and have a look, I would be happy to show you and explain in detail. (My contact details are on the blog) I have a very good monitoring system so can show you in depth figures.

Hi, thanks for your reply. We were looking into getting solar panels when the ECO4 deal popped up, so your comments are very useful! Lots of companies on fb were/are offering the fully-funded HP/insulation/solar panels deal for people on benefits or low income (less than £31k) in properties energy rated D or below that are not on mains gas. It doesn't specifically say on this ad (the first one I found!) but the funding goes up to £30k. The intention seems to be to bring the least efficient homes up to a sensible standard. Some of the companies are cherry-picking properties - I have friends who live in an old farmhouse with stone walls and leaky windows; they applied but none of the companies would touch them. JamesPa commented on this thread about what he calls "grant harvesters" - I guess they're doing the "easy" properties. Whether anything can be done about properties like my friends', I don't know. 

This hub has been incredibly useful for me - I didn't know much about heat pumps, and a lot of what I'd read in the media was pretty negative, but comments on here have made things much clearer. I still haven't decided whether to go for it, but I've got a much clearer idea of what answers I need when they come back to me with the proposed package. Either way, we're definitely going to get solar panels, and there are grants available. It's so easy when you're at the wrong end of the learning curve to be bamboozled by unscrupulous companies, and I was always taught that if something looks too good to be true, it IS too good to be true, hence my hesitation - but actually this one does seem to be a good thing!

Thank you for replying!

Posted by: @cookie197

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I have friends who live in an old farmhouse with stone walls and leaky windows; they applied but none of the companies would touch them.

This is another persistent myth that needs to be dispelled. A building does not care one bit where the heat that heats it comes from. It is perfectly possible to fit a heat pump to an old poorly insulated leaky stone building, I have done it, and by and large it has been a success. You may need to fit larger rads, I had to, to accommodate the lower LWT, but again, a lower temp system doesn't care where the lower LWT heat comes from, whether it is a heat pump or a fossil fuel boiler running at lower temps. As well as possibly fitting larger rads, you certainly need to do what you can within any constraints eg being a listed building, to improve insulation and reduce leaks. 

The only thing that isn't a myth is that older poorly insulated leaky buildings cost more to heat. But that applies whatever the heat source.