What KW rating for our heating?

Discussion in 'Plumbers' Talk' started by Dam0n, Aug 7, 2017.

  1. Dam0n

    Dam0n New Member

    Hi everyone, back again with another question for the Gurus on this forum.

    We are in the process of buying a boiler for our water + CH system and being an all electric setup its a new area for me.

    The boiler is being custom made as it is to accept a log burner back boiler and solar thermal panels (when fitted) to help keep the running costs down. The boiler is a thermal store setup and to the best of my knowledge a completely unvented system.

    I've attached the spec of the boiler below -

    My main question is -
    Is the specified 9kw rating large enough for the heating?
    Is 3kw for hot water enough?

    The cottage has one radiator downstairs + three radiators upstairs along side wet underfloor heating throughout the main body of the house at ground level. Again, I'll attach a image of the layout and size of the house to this post.

    Thanks very much,


  2. CraigMcK

    CraigMcK Well-Known Member

    I thought thermal store tanks used the same heat source for the stored hot water? So don't understand why it specifies a heating / hot water element, unless it allows them to use the smaller element in summer when the heating may not be on

    Anyway, water heats based on volume in litres x 4 x temperature rise in degrees centigrade / 3412 = kw to heat in 1 hour, so if the tank volume is 200l and it's cold ~ 15C and you want it up to 60C = 200x45/3412 = 10.5kw. If you only use the 3kw element it will take 3 and a bit times longer.

    Someone else may have a better knowledge of how these work, but the maths remains the same,just different inputs.
    Dam0n likes this.
  3. Dr Bodgit

    Dr Bodgit Well-Known Member

    Def not an expert here, but as a guide....I have a 3 bed semi. The boiler is 18Kw (compared to your 9kw) and the electric immersion heater element (which I rarely use) is probably 3Kw also. So yours will do the job, but hot water will take a while to heat and you may struggle to get the house warm n cosy.
    Dam0n likes this.
  4. kiaora

    kiaora Active Member

    If you can imagine having 9 x 1 kilowatt electric fires around your house, and you think it's going warm you up, then the system. Will be ok.

    That answers your first question, ( or, do a whole house calculation)

    3 kw is the normal allowance got hot water,

    And yes it will be good to have solar wood burner to feed the thermal store, but with solid fuel NEVER use UNVENTED cylinder, (you can't turn it off) and they can go bang!
    Dam0n likes this.
  5. The Teach

    The Teach Active Member

    9kw does not sound enough,your ufh will use heated water lower than the radiators but will be in use longer.

    There are online calculators for wet ufh and for wet radiators,maybe do a calculation.

    Sounds like your system will be tailor made for your property,who is installing the system ?

    Dam0n likes this.
  6. Dam0n

    Dam0n New Member

    Thanks for the replies.

    TT, the setup is going to be custom built for the property. I haven't got an installer as of yet as I plan to get the unit delivered and in place with relevant feeds ready to be connected up. The 9kw rating is what the company who makes the boiler suggested ( i sent over the same details as the original post) but they stated that they only manufacturer the units and I would have to get someone in the know to do the calculations.

    Is there anyone here that can do the calcs for me? I dont mind paying with beer :) I can supply any info needed. desperate to get the unit ordered before it turns cold and nasty again.

    Thanks again for your input everyone

Share This Page