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Heating and cooling: Any downsides to replacing regular boiler with combi?

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    Our current heating system is a dodgy DIY job (regular boiler, 2 hot water tanks, very odd plumbing). The boiler is a year old.

    We need a new bathroom and the fitter has strongly recommended we replace the heating system first as a) it is likely to go wrong and need work which might well involve digging into walls etc, so it's better to do that before we have a new bathroom (and plastering in other parts of the house) done. b) switching to a combi boiler would free up much-needed space in a relatively small bathroom.

    I'm aware that we won't be on a gas boiler forever. My question is - is there any benefit to maintaining space for the hot water cylinder in the bathroom on the basis that we might need to move back to tanks if we move to e.g. an air source heat pump? The heating engineer said that's probably 20 years away in our 1930s house. We have a second (120 litre) tank in the crawlspace, which we'd keep either way (just because it's too much hassle to get it out!).
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      CommentAuthordjh
    • CommentTimeOct 3rd 2023
     
    Personally I would try and find space for a tank (either cylinder or thermal store) since it can be heated by solar PV much of the time. If you're planning to replace the heating system then I'd suggest designing it so it can be powered by a heat pump, even if you choose to use a gas boiler initially. A common problem when considering installing a heat pump is that the heating system hasn't been designed with it in mind and there is a lot of work and associated mess to make it suitable. So if you're anticipating some mess, you may as well do it just once.
    • CommentAuthortony
    • CommentTimeOct 3rd 2023
     
    Old taps and rad valves can start leaking when used at higher pressures than previously, you will loose an airing cupboard, the background heat loss from a HW cylinder warms the house a little and you might miss that , higher water use due to higher flows of hot water = bigger bills
  4.  
    On the green building forum I don't think anyone should be considering fitting a gas boiler now - we're really at the stage where it's obvious that is not green, sustainable or a long term strategy.

    Surely if you're replacing the heating system now is the time to think about fitting a heat pump.
  5.  
    Thanks everyone, I really appreciate your thoughts.

    Posted By: Simon StillOn the green building forum I don't think anyone should be considering fitting a gas boiler now - we're really at the stage where it's obvious that is not green, sustainable or a long term strategy.

    Surely if you're replacing the heating system now is the time to think about fitting a heat pump.


    Simon, I take your point. The heating engineer I spoke to said our property wouldn't be suitable in its current state as it's not well insulated enough. It's a 1930 with cavity wall insulation, but I think a solid wall on the front (I'm trying to address that through ECO4). We have underfloor insulation and an insulated loft conversion (albeit to 1980s standards). We can't afford a big increase in energy bills at the moment. Any recommendations for where to get a balanced opinion on suitability? All the people I can see locally either do gas boilers or air source heat pumps, so I'm assuming have a bias.
    • CommentAuthorSimon Still
    • CommentTimeOct 4th 2023 edited
     
    Posted By: DannySheffieldThanks everyone, I really appreciate your thoughts.

    Posted By: Simon StillOn the green building forum I don't think anyone should be considering fitting a gas boiler now - we're really at the stage where it's obvious that is not green, sustainable or a long term strategy.

    Surely if you're replacing the heating system now is the time to think about fitting a heat pump.


    Simon, I take your point. The heating engineer I spoke to said our property wouldn't be suitable in its current state as it's not well insulated enough. It's a 1930 with cavity wall insulation, but I think a solid wall on the front (I'm trying to address that through ECO4). We have underfloor insulation and an insulated loft conversion (albeit to 1980s standards). We can't afford a big increase in energy bills at the moment. Any recommendations for where to get a balanced opinion on suitability? All the people I can see locally either do gas boilers or air source heat pumps, so I'm assuming have a bias.


    I think there is a big issue with heating engineers repeating the scare stories from the press or that they've been fed by the boiler manufacturers who have a clear incentive to discourage heat pump sales.

    This thread (on Twitter) says the sums add up right now both for capital and running costs of a heat pump -
    https://twitter.com/janrosenow/status/1709555750291263846?s=46&t=dAsKuC7CSc6zyBFbJ0vjeQ

    Capital costs only add up because of current subsidies but running costs:
    "This means that already with a modest SCoP of 2.9 at current price cap electricity prices the running costs of a heat pump are a bit lower than a 85% efficient gas boiler. With existing time of use tariffs or the new
    @OVOEnergy @_heatgeek offer much larger savings are to be had even at modest SCoPs. High SCoPs and those tariffs savings combined could be more than half of the running costs of a typical gas boiler.
    • CommentAuthorSimon Still
    • CommentTimeOct 4th 2023 edited
     
    Also - slightly unrelated - but this guys videos look fascinating - a really smart, forward thinking, heating engineer (who fits and recommends heat pumps).

    I've only just skipped through this one but he made huge savings by scaling back an overspeed heating system and adding weather compensation control. House had TWO oversized boilers, two 300l tank and excessive pumps....
    https://www.youtube.com/watch?v=FaSHX5mhyDw
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      CommentAuthordjh
    • CommentTimeOct 4th 2023
     
    Seems like a good guy. I only watched the first five minutes but he did seem to be thinking about everything quite sensibly. His company website is at https://www.urbanplumbers.co.uk/
  9.  
    There's a little community of forward-looking installers who overlap around the Heat Geek and Open Energy Monitor groups
    Eg
    https://twitter.com/Damon_BPHR
    https://twitter.com/Ainsdale_Gas
    https://twitter.com/GSHPinstaller
  10.  
    Danny, the kind of cylinders they use with heat pumps might not be the same as the ones you already have (much bigger internal coils). They might also like them to be located close to the heat pump, because the connecting pipe needs to be bigger bore than previously and is quite expensive per m. This may influence your decisions on your existing tanks.
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      CommentAuthordjh
    • CommentTimeOct 5th 2023
     
    Twitter links are pretty useless these days, assuming you don't have an account.
  12.  
    I agree, but small companies seem only to discuss their work and new ideas with each other on Twitter, or else on Facebook. Not sure which is least bad.

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