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Radiator sizing

Discussion in 'Plumbing and Central Heating' started by askman, 2 Jan 2018.

  1. askman

    askman

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    Does anyone have a link to a radiator sizing calculator which they've found to be reliable?

    I've got a 3.5 x 3.5 x 2.5m bedroom with a small adjoining closet and roughly 2sqm double glazed window which I need a rad for and the calculators I've used come up with vastly different results, ranging from 2500 to 4300 btu/hr...

    Granted it'll have a TRV so I can afford some oversizing, but the difference in figures suggested is startling.
     
  2. D_Hailsham

    D_Hailsham

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    Try Radiator Calculator

    Many calculators use "rule of thumb" methods, e.g "volume x 5", which have no scientific basis.
     
  3. Terrywookfit

    Terrywookfit

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    Type and no of external walls?
    Floor construction?
    Required temperature. Would be handy.
     
  4. askman

    askman

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    Have you used this one for an actual install? I tried it earlier and was giving figures towards the lower end of what I've seen.

    1 no. external wall - approx 4.3m long including the closet.
    2 no. party walls (mid terrace house) and the other walls are internal in my house to heated spaces
    All external and party walls are solid brick ~200mm.
    Well insulated loft to above, and heated living room below
    Delta T is 50C
     
  5. Terrywookfit

    Terrywookfit

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    I would be sizing that around 5000 btu/hr.
    Quicker and guaranteed warm up. A TRV will control temp,
     
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  6. D_Hailsham

    D_Hailsham

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    I haven't looked at the program for a long time. It has changed a lot and is not giving the answers I would expect. I can't find out why, so I will not be recommending it any more.


    I ran this info through Stelrad Stars V3 and it came up with 1288W. That assumes 21C internal and -1C external; also one air change an hour (2 changes = 1603W).

    So Terry is not far out; I wonder what he used - experience or a calculator?
     
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  7. Terrywookfit

    Terrywookfit

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    A quick guesstimate. 11.5 x 11.5 x 8 x5 =5290.

    I would of course consult my faithful "Mears" to be sure!!

    It is better to be over than borderline.
     
  8. Mears would give about 6100 assuming you include the cupboard in the calculations, and 5400 without it. The insulation in the loft, and the heated room below it would help cut down the requirements, so I'd go with 5500.
     
  9. Hot&Cold

    Hot&Cold

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  10. D_Hailsham

    D_Hailsham

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    Well, well well!

    BTU = Volume (cu.ft.) x 5 !!! I remember seeing that on a rad manufacturer's spec sheet in the early 1990's. I think it originated in the Gas Board, when they had a monopoly, who were selling heating systems with "guaranteed temperatures".
     
  11. But what was the guaranteed temperature. My parents had the first CH system in our street, and the installers wanted to set the bedrooms and bathroom at 60F, and mum insisted that getting out of a hot bath naked into a cold room, wasn't conducive for good health, and made them set the whole house at 70. They weren't happy, but they did it. She also got a valve fitted in the garage that opened up the heating to the bedrooms, so about half an hour before bedtime, we had to go in the garage and turn this dirty great lever, as there wan't anything small and fancy in those days - very industrial it was.
     
  12. DIYnot Local

    DIYnot Local

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