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Gas boiler upgrade - 25kW or 32kW

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  • 24-11-2023 11:11am
    #1
    ian123
    Registered Users Posts: 25 ✭


    I have an aging Baxi Potterton 60/100 IE boiler - rated at ~32kW - 2 heating zones + hot water (installed 2005)

    Have had some quotes for replacement condensing boiler - most pitching a 25kW/28kW alternatives (Viessmann 100, Ideal 28).

    there are 16 radiators connected today - will be adding 1 more with upgrade.

    Does it make sense to go for a 25kW boiler or should I insist on matching the ~32kW capacity of the existing boiler (eg the 32kW Viessmann 100) ?

    Ian

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    #2
    antoinolachtnai
    Registered Users Posts: 9,776 ✭✭✭antoinolachtnai


    It’s not the number of radiators that matters. It’s the heat loss of the house on a very cold day that determines how big a boiler you need. This depends on the insulation, whether the house is detached and so on.

    If the boiler you have runs continuously for hours on end to heat the house you need the bigger boiler. If it heats up pretty quickly then the smaller one will probably be fine. But it’s hard for anyone to say without having seen the house.



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    #3
    10-10-20
    Registered Users Posts: 6,785 ✭✭✭10-10-20


    I concur with what @antoinolachtnai says and I'll add that the reality these days is that many houses have also upgraded insulation and windows as well as getting walls pumped since the original install, so the demand on the boiler (through heatloss) can be fair bit lower. So if you house has had extensive upgrades such as those mentioned then the heatloss is now lower and therefore you may be able to operate off a smaller boiler thank was originally installed. Also don't forget that when choosing the boiler the original installer was working of a heatloss value and they then picked the next largest boiler, so there may have been some heatroom in that boiler's capacity in the first place.

    Anyway, the right answer here is to perform a heatloss calculation and work off that value for the boiler.



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    #4
    mcgragger
    Registered Users Posts: 439 ✭✭mcgragger


    what kind of prices are you getting?



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    #5
    ian123
    Registered Users Posts: 25 ✭ian123


    Varying from 2970 to 6000. Some of the quotes have extra work (eg power flush, extra flue, upgrade 1x rad, alarm, replacement valves)

    I ended up taking a ~5k option based on a vitodens 100/25kw option. not installed yet



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