Next steps with home renovation, heat pump?

So we are planning to have an extension built and would like underfloor heating as an alternative to radiators.  We currently have a 5 year old boiler that my plumber says will be capable of running the newly proposed underfloor wet heating but I am considering the next few years and overhauling the whole system with a heat pump to heat the water instead of the boiler but could I replace the boiler and just have a heat pump do everything including hot water?  We have no water tank currently as we have a combi boiler but as we are renovating it seems an ideal time to get it all done in one go, otherwise if we decide to do something later we might have to reconfigure pipes etc which won't be the easiest of job.

Secondarily we currently have solar PV for electric generation and don't store our generated power, have not plans for an electric car and don't use it to heat water, so could the excess be used in conjunction with the heat pump to make more efficient use of what is being generated.

Then there is a question of a/c, with the climate warming up I would like to consider putting air conditioning into the bedrooms (x4) of the house, would an air source heat pump be able to do this as well?

Anyone know of a recommended product to do this or set of products or has a working system that does this?  Looking for ideas of cost.

If this is a big vague let me know what other details are needed, not particularly looking at payback at this stage more interested in what solutions are available and anyones recommendations based on experience.



  • matelodave
    matelodave Posts: 8,606 Forumite
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    edited 15 June 2020 at 11:01AM
    TBH I'd stay with a gas boiler, it's still a lot cheaper to run than a heat pump - even if you can get leccy at 12p/kwh and attain a COP of 3 it will cost you 4p/kwh which is still more expensive than gas.

    To achieve maximum efficiency you've got to revamp the whole heating system to run at low flow temperatures (35-40 degrees) so the costs are quite high. You will get some back in the way of the Renewable Heat Incentive but it's not a Kings ransom (I'll get about £5k back over 7 years for mine). You'll need a hot water tank as heatpumps don't work like conventional boilers and you need to operate them properly to maximise their benefits.

    As far as I can determine the biggest problems that people have with heatpumps is that they tend to be under specified, bunged onto existing systems, not planned properly and most of all not used correctly so you really do need to do a lot of research to understand what you need and what you want to achieve

    Generally you need most of your heat in the winter when the days are long, the sun doesn't shine and their efficiency is at their lowest so I don't see that they match the energy provision of solar panels which produce most in the summer and least in the winter. The government stopped the FIT scheme for solar energy a year or so back so the only options you have are to try and use all you can or try and sell some back to one of the energy companies (you need to find out who is giving the best deal and for how long)

    You can get reversible heatpumps which heat and cool, likewise you can get fan-coil units which will either heat or cool and blow the air about or even a split aircon system with multiple air units.

    There are a lot of options, all of which are likely to be quite expensive so you really do have to do a lot of very careful sums to decide whether the cost and benefit is worth it all.

    We refurbed our bungalow 10 years ago and decided at the outset to put u/f heating all over and install a heat pump and we reckon it's probably paid for it'self in terms of lower energy bills and the RHI.  BUT - we don't have access to mains gas, so the alterniatives were LPG, OIL, Biomass or replace the storage heaters. Had gas been available then the heatpump wouldn't have been even considered. It does provide our hot water quite cheaply in the summer but I'd still be tempted to put in gas if they did decide to run it up our road (highly unlikely as we live a long way from the nearest gas main and we've got a river between us and it)
    Never under estimate the power of stupid people in large numbers
  • Pulpdiction
    Pulpdiction Posts: 228 Forumite
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    Thanks for the response, some valid points.  I guess for me I have three main areas to address:
    1. 60sqm of underfloor heating going in the extension, so my current gas boiler can manage this alongside the other heating requirements.
    2.Like to add a/c at some point.
    3.Like to make better use of solar generated and not used.

    I have been looking at the LG therma range and it looks like it can do the heating and the cooling, so I think it could cover all of the bases, but I could retro fit a heatpump and take out my boiler at a later date, so no rush, just annoys me that I'm wasting the generated electricity, being on FIT and an assumed 50% export then it's money down the drain.

    Was alternatively thinking could get a hot water tank and use that to feed the combi, so divert the solar to heat that when there is generation available and heat the water up so the combi might not need to kick in for some of the day/morning showers, then could swap out the combi later with a heat pump once they come down a bit more in money.  But having said that the ones above are around £3.5k starting price, plus install.  Batteries are still beyond the sensible in terms of using them to store what is generated due to price, so hot water tank seems to be most sensible option.

    Other point is that if I can get one device that does it all it saves buying a separate a/c system.  

  • matelodave
    matelodave Posts: 8,606 Forumite
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    As I said, do your sums - I dunno what size your house is or the heat losses but I'd bet that you can't get one of the size you'd need for the whole house for £3.5k. Add in the price of a decent water tank (probably at least a grand) plus other stuff.and I doubt you'll get much change out of £6-8k. You really do need to do a cost/benefit analysis to ensure that you dont end up in a spiral of diminishing returns

    I really dont know how much you spend on say just hot water but in my case with a heatpump it's around 20p a day at this time of the year, posssibly 30-35p a day in the winter which is around £100 a year. Say you spend twice that because you might be more profligate with your hot water, it's still going to take you a really long time 6000/200 = 30 years to recover the cost and if you dont get enough solar energy to cover 100% then you'll have to supplement it from the grid and as i said in my previous post, even heatpump leccy costs more than mains gas

    I did explore solar thermal when I installed my heatpump but the installer pointed out that the £1500 cost would take 15 years to pay back if I was only spending £100 a year or less on heating water anyway

    Even just installing a tank with all the associated plumbing and a solar diverter to recover 50% of your generated capacity will probably take 3-5 years to recover the cost. I know it may be great to be green but can you really afford it because it's can have a really long term payback period and you don't know whats going to happen between now and then. 

    In the end it's your choice and it might give you a fuzzy warm feeling to go a bit greener but don't think that all these magic devices are going to save you money especially in the short term.
    Never under estimate the power of stupid people in large numbers
  • Gerry1
    Gerry1 Posts: 9,936 Forumite
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    edited 15 June 2020 at 2:59PM
    You should also consider that a weird and wonderful system may not increase the value of your house by the amount you paid.
    It might even deter some purchasers (and their surveyors) who would expect a conventional gas boiler system and would look at a heat pump as though it were a collection of Fischer magic dust radiators !
    Bit like a swimming pool, some would love it, others would imagine drowning kids and maintenance costs etc and would hate it.
  • Pulpdiction
    Pulpdiction Posts: 228 Forumite
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    Thanks both, I think what I'm concluding is the longer I wait the cheaper it is likely to get, I think we'll see some read drops in prices when heat pumps start to replace fossil fuels in new builds from 2025 and if my boiler can keep going for that long then I guess I've had my money's worth out of it.  So the key decision point either comes when my boiler dies, the price of energy goes up significantly or global warming forces me to buy air con.  
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