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Boiler size Help required

Discussion in 'Plumbing and Central Heating' started by ScotchGas, 19 Sep 2011.

  1. ScotchGas

    ScotchGas

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    I'm replacing a back boiler with a combi boiler for a work project (i'm an apprentice) and I have calculated the radiator output from using their sizes and checking them against radiators from TDL - Trade Distribution Ltd, with all 6 adding up to 8.27kW. Its a bungalow house so i knew the figure would be a bit lower but i was just wondering if their was anything else i need to take into account like how systems req 3kW for hot water. I have just came into the combi boiler module so dont know all the logistics.
    Thanks anyone who can help.[/b]
     
  2. muggles

    muggles

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    You don't need to add 3kw for a combi boiler, combi boilers are generally sized on hot water demand and the performance of the water main rather than the radiator heat output requirement
     
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  4. D_Hailsham

    D_Hailsham

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    You are making the false assumption that the radiators are correctly sized.

    Current practice recommends using a whole-house Boiler Size Calculator.

    However, as you are installing a combi boiler, this has to be sized for the HW requirement. This means measuring the incoming cold water and pressure. A boiler needs to deliver 2.5kW for each litre/minute to raise the temperature by 35C. So a 40kW boiler will handle a flow rate of 16 litres/min.
     
  5. ScotchGas

    ScotchGas

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    Thanks for the help, its just a written project so i have to just assume the rads and pressures are all correct. Going to go with a 24kw for it going by whats been said
     
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