Sizing a boiler

Discussion in 'Plumbing and Central Heating' started by whistler, 4 Oct 2020.

  1. whistler


    3 Jul 2006
    Thanks Received:
    United Kingdom
    My current boiler is a vaillant turbomax 824 which I presume is a 24kw output.

    Its getting quite old now so considering having it replaced with a similar current vaillant model.

    Since the boiler was installed, two additional small radiators have been added.

    I measured all the rads in the house and got an approximate output for each one and totalling this up it came to around 35kw.

    Most of the rads are controlled with a Honeywell Evohome zoned system, so it is unlikely that all rads will be open at the same time, and the system heats the house satisfactorily.

    If I go for a new boiler, should I upgrade to something higher than 24kw or would I be just wasting money?
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  3. D_Hailsham


    18 Oct 2007
    Thanks Received:
    United Kingdom
    The required size for a boiler is determined by the heat loss from the house, not by the sum of the radiator outputs.

    The turbomax is a combi boiler (instant hot water - no HW cylinder) so the size of boiler is determined by the hot water requirement.
    35kW is a lot. Post a list of what you have - length, width, type (21, 22 or L1, K1 etc) - and some one will work out your actual radiator output.

    A decent engineer will carry out a heat loss calculation before saying what size boiler you need..
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    United Kingdom

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