Electric boiler capacity?

Discussion in 'Eco Talk' started by rbrian, Sep 4, 2021.

  1. rbrian

    rbrian Member

    I live in a tiny 40m2 house, with pretty good insulation, double glazing, solar panels. Now I want to replace my gas combi boiler. I have no outside space, so a heat pump isn't an option. An electric boiler seems like a simple replacement, but on single phase electricity I can only get a 9kw one. That doesn't seem enough to replace my 24kw boiler!

    Perhaps I'll have to get an electric shower, in which case it might make more sense to get rid of the boiler entirely, freeing up a cupboard in the kitchen, and fit electric heaters, perhaps infrared panels. In that case, what about the kitchen tap?
     
  2. rbrian

    rbrian Member

    Having looked at it a bit more, it would need a new electric feed to the boiler, which with a concrete floor is a big hassle. I'm starting to see why people want hydrogen to work (it won't, I'm not falling for that greenwash). I think I'll get an electric shower, and electric heating. What about the kitchen tap though? Another electric shower?
     
  3. Could you not go 9kw that also feeds a small unvented cylinder for hot water rather than I'm guessing the combi you already have? EHC boilers you can turn down the capacity based on power restrictions and they work well. Do a heat loss calc and depending on heat loss 9kw with some radiator changes may work well
     
  4. rbrian

    rbrian Member

    Thanks for the tip! Evidently I should have spent more time researching. Now all I need to do is figure out how best to run a new power cable - the current 6 amp feed to the gas boiler isn't enough, it'll need 10 times as much, and a much thicker cable. Probably lifting the floorboards upstairs will be the easiest way.

    This one looks like a good choice:
    https://www.elnur.co.uk/product/mattira-wall-mounted-electric-combi-boiler/
     
  5. Mike83

    Mike83 Screwfix Select

    Get a new combi.
    Then next time make the leap into something else. Things will have moved on a fair bit and other technologies will hopefully have been tried and tested.
    Sticking with gas will be cheaper for the next few years.
    If the combi works for you just now then you may not be happy with what any changes brings.
     
  6. rbrian

    rbrian Member

    My house is tiny, fitting a separate tank isn't ideal - it could go in the loft, but there aren't any pipes up there, so it'll be a big job. I'd rather get something that fits in the same kitchen cupboard as my existing combi. The one I linked to is expensive, but it's the only one I've found that's small enough and also sufficiently powerful.
     
  7. rbrian

    rbrian Member

    I don't actually need a new boiler, it's only 8 years old and running fine. I want to stop burning fossil fuels.
     
  8. Bob Rathbone

    Bob Rathbone Screwfix Select

    They burn fossil fuel to make electricity in plant that is far less efficient than your combi boiler, stick with gas, save mone and save the planet. Don't be drawn in by all of the carp concerned with burning fossil fuels, until we go 100% nuclear, wind and water electricity generation will continue to pollute.
     
  9. rbrian

    rbrian Member

    Scotland already has more than 50% wind generation, and I have solar panels. The grid is only going to get cleaner, my boiler won't.
     
  10. Bob Rathbone

    Bob Rathbone Screwfix Select

    Today on the red button I read that the UK has re commissioned a coal fired generating station due to the increase in the cost of gas. I challenge your assumption that the 'Grid will become cleaner' especially in the near future before reliable alternative energy, such as nuclear, becomes available in large quantities. Wind and solar are great, when the sun shines and the wind blows, but how do we fill the times when wind and sun are not available, batteries must be charged and that energy will be taken from the available energy in the grid. The only benefit you will feel from changing from gas to electricity will be a much larger heating bill, at this time it will not contribute to reducing Co2 emissions overall, it will just move the Co2 to someone else's back yard.
     
    Last edited: Sep 7, 2021
    stevie22 likes this.
  11. Jimbo

    Jimbo Screwfix Select

    The grid de-carbonisation is well documented. The CO2 per kWhr has halved in the last decade and is forecast to halve again in the next. Reducing the carbon intensity of gas is much more difficult.

    How the UK transformed its electricity supply in just a decade | Carbon Brief

    To the OP, if you need this kind of thermal load, electric will cost a fortune to run. The only real option would be a heat pump, which will cost 1/3rd or less to run, compared to an electric boiler. However a gas boiler will still be cheaper to run at the moment unless you have entirely underfloor heating.

    At 233g per kWhr currently, a heatpump operating at SCOP of 3 would be generating about 75g per kWhr, which is close to one third of the CO2 produced by a gas boiler.
     
    rbrian likes this.
  12. quasar9

    quasar9 Screwfix Select

    24kw boiler for a small house is quite a lot, especially if it’s well insulated as you say ! If in CH mode it only runs a few minutes in the hour, you are not using much fossil fuel in the first place . Do remember, gas heating is pretty efficient, especially with modern condensing boilers. In any case electricity is 5x more expensive then gas for the same kilowatt of heat but it’s a decision for you to make.
     
  13. Jimbo

    Jimbo Screwfix Select

    Look at a heat pump. The RHI scheme is still open and will pay a significant proportion of the cost (all of it in some cases).
     
  14. rbrian

    rbrian Member

    A heat pump isn't really an option. It's a new build (8 years ago) estate, with communal grass outside, which is nice because somebody else mows it, but laying a pipe under it will need an awful lot of paperwork. On top of that, it's a tiny house - in some areas it would have had a hot water tank, but that cupboard is my tool cupboard, and I don't really want to empty it. Still, nothing is impossible. My house is well insulated, so I don't think the cost of electricity will be too bad - probably still under £100 per month if my calculations are correct. I'm also looking at infrared panels, which heat thermal mass, not air, so can make you feel warm enough with half the energy. I'm certain that would be affordable, more so if I invest in a battery so I can use the energy my east-facing panels generate in the morning in the evening. Many people have electric showers and don't complain about the cost - I'd quite like to change to that, and dump the boiler entirely, freeing up a large kitchen cupboard. I'm not sure what to do about the kitchen and bathroom taps though.
     
  15. Jimbo

    Jimbo Screwfix Select

    I meant air source heat pump. It would be just a small box outside. No digging.
     
  16. rogerk101

    rogerk101 Screwfix Select

    Why do you think you are limited to 9kW supply?
     
  17. It's pretty likely that the Government will play with the tax on gas and electric in the bear future. Moving it all to gas will give nearer price parity but not really change total bills for most.

    You can get air to air heat pumps that look like air conditioning units.
     
  18. Jimbo

    Jimbo Screwfix Select

    Air to air doesn't qualify for RHI though, only air-to-water.
     
    Starslikedust likes this.
  19. rbrian

    rbrian Member

    Almost very one I've seen is limited to 9kw on a single phase supply, though I did find one that went up to 11kw - but any more requires 3 phase electrics.
     

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