Viewing 18 posts - 1 through 18 (of 18 total)
  • Heat requirement for kitchen diner – check my calcs, please
  • Bimbler
    Free Member

    I’ve used a lot of the online heat calculators and they all show a heat requirement of about 5kW. Builder insists it will be lower so using u values and areas I’ve got a heat requirement of about 2.5 kW – now I worry I’ve done something wrong

    Area m2 u value
    windows 23.74 1.7
    walls 27 0.3
    roof 34 0.25
    floor 60 0.25

    Would someone be so kind as to check the calculations please.

    *grumble bloomin formatting

    newrobdob
    Free Member

    I have the same problem in my new kitchen diner. Hang the normal online calculators I get a requirement ofaout 10,500 BTU. It’s a big room – 7.5m long and between 4.5 and 3m wide. I can only put rads in certain places so I’m going for a big one under the window of around 9000 BTUS and another opposite of around 3000 BTUS. Don’t know if that is the best way to go but I reckon that’ll give nice even heat around the room.

    poolman
    Free Member

    Sorry i have no idea but what i do is ask someone who knows, my plumber usually, and overspec what he recommends, cooling or heating. I reckon like a car a bigger engine ticking over is more efficient than a smaller one at full tilt.

    Worked so far no problem.

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    Scienceofficer
    Free Member

    Why is your ceiling so much smaller than your floor?

    Bimbler
    Free Member

    Why is your ceiling so much smaller than your floor?

    It’s an L shaped extension going out at the back and side, and encompassing our galley kitchen and dining room, so the “missing” roof is internal,not sure it’s worth adding that to calculation?

    captainsasquatch
    Free Member

    I don’t understand the question. I don’t know who said what or who arrived at which conclusion. 😕

    Bear
    Free Member

    Are you subtracting the window area from the wall area?

    also seem to have a large area of glazing so heat loss will be big.

    lesgrandepotato
    Full Member

    New build then judging by the u values? Decent quality windows and properly insulated cavities and floors for that.

    newrobdob
    Free Member

    If floor is 60m2 then that’s a 10m x 6m room. Or other multiples that make 60. Which is massive.

    Think about it. 2.5kw is a 2.5 bar electric fire to heat that whole room. That doesn’t sound like enough to me.

    giant_scum
    Free Member

    Have you considered a wet plinth heater for the kitchen?
    We have one and it is good, handy for drying the dogs of as well!

    glasgowdan
    Free Member

    Just get 2 big or 3 medium radiators and stop getting bogged down in theory 🙂

    tjagain
    Full Member

    Poolman – surely an over specced boiler that is not working hard ie cycling on and off all the time is wasteful and less efficient?

    Nobeerinthefridge
    Free Member

    Like stop start in cars?

    tjagain
    Full Member

    Not really ‘cos the boiler will not be working efficiently when its continually heating up and cooling down surely?

    Bimbler
    Free Member

    :sigh: the omnipotence of STW has been sorely challenged

    As far as I understand it you can calculate the heat requirement of a room by working out the heat loss using the u-value or thermal transmittance of the materials in the wall floor etc

    So if you know the size of the barrier and the amount of heat it loses per sq metre you can work out the total heat loss.

    So I have 24m2 of windows, the u-value of these is 1.7, so 24*1.7= 40.8

    27m2 of walls, u-value of these is 0.3 (probably less but not more) 27*0.3=8.1

    34m2 of roof u value is 0.25 (again probably less) 34*0.25=8.5

    60m2 of floor u value 0.25 = 15

    Add them all up I get 72.4, bung on 25% for ventilation = 90.5

    Then I need to multiply this by the probable temperature gradient so if it’s -5° outside and I want it to be 21° inside that’s a difference of 26.

    So 90.5 * 26 = 2353W (is that watts or what, it’s something)

    Apologies, I’m not a maths head, typical B at o-level type bod which is why I need someone to critique these calcs.

    Looking to get trench radiators (f’n expensive) and plinth heaters

    lesgrandepotato
    Full Member

    I think the Calcs are right – but unless its a new build I’d question your U values.. I’d also query the temp gradient assumption to the floor – whats the ambient soil temp? won’t be the same as the air.

    I’d also question the areas – you have twice as much floor as ceiling. This seems unlikely unless its partly outside?

    Similarly you have 24m2 of windows and 27m2 of wall – is it a conservatory? or are a large amount of windows in the roof?

    Bimbler
    Free Member

    I think the Calcs are right – but unless its a new build I’d question your U values.. I’d also query the temp gradient assumption to the floor – whats the ambient soil temp? won’t be the same as the air.

    I’d also question the areas – you have twice as much floor as ceiling. This seems unlikely unless its partly outside?

    Roof is basically 150mm of celotex and 36mm (2*18mm) of plywood

    walls are thermalite blocks (surprisingly hard to get hold of) and 100mm of celotex.

    Floor is suspended wooden floor with 100mm of celotex (I think, have to check on that one)

    Extension is L shaped going out 3m at back and 3 metres at side in. So yes partly outside and partly “inside”. The outside walls are all new build.

    The room is 8mx8m roughly with 6m2 utility room, which will be heated separately.

    Window U Value I took from manufacturers blah-di blah. Windows made up of 6.7*2.6 bifolds, 3*1.2m*1.2m roof lights and a kitchen window.

    Pleased to be critiqued, don’t want to spend 10k on a new heating system and the damn place ending up cold, nor do I want the boiler short cycling all the time.

    lesgrandepotato
    Full Member

    Seems about right to me then – there are a few online calcs you can try – from memory our downstairs space was circa 10kw to heat which seems proportional to your space.

    Windows may be describing the pane performance, not the pane and frame performance – may be worth a check.
    1.7 is a normal/good double glazed average figure from memory

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