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Reliable gas boiler calculator that included the rad sizes and quantity

  • 06-11-2021 11:50am
    #1
    mistermarantz
    Registered Users, Registered Users 2 Posts: 50 ✭✭


    Hello. Is there a reliable online gas boiler calculator that also considers the size of the rads?

    The house is 3000 square feet with 22 rads of which most are doubles and a lot of them are around 1500 length (8 of the rads were recently changed to bigger ones). The existing boiler is a 35KW system but needs replacement.

    I've received several quotations and all are recommending 30-32KW boilers but in my opinion the previous 35KW boiler never adequately heated the place.

    Any help welcomed!



Comments

  • #2
    Wearb
    Moderators, Home & Garden Moderators Posts: 6,383 Mod ✭✭✭✭Wearb


    What's your BER?

    Please follow site and charter rules. "Resistance is futile"



  • #3
    mistermarantz
    Registered Users, Registered Users 2 Posts: 50 ✭✭mistermarantz


    https://www.boards.ie/discussion/comment/118126935#Comment_118126935

    Not sure. Probably a C3. The house is around 20 years old.



  • #4
    Borzoi
    Registered Users, Registered Users 2 Posts: 2,876 ✭✭✭Borzoi


    Off the top of my head, 36kW should be perfect. But equally, you shouldn't notice the difference down to 32kW except on a very cold day. That leads me to suspect that there is other issues - poor circulation, undersized rads, poor insulation or drafts. C3 isn't bad, but doesn't match the output number



  • #5
    mistermarantz
    Registered Users, Registered Users 2 Posts: 50 ✭✭mistermarantz


    https://www.boards.ie/discussion/comment/118127022#Comment_118127022

    Yes definitely we had an issue with undersized rads so I got 8 of them changed. A drafty door was recently changed also. Unfortunately the existing boiler broke as soon as the weather cooled and therefore have not been able to test out 35KW on the new larger rads. I want to make sure I don't underpower the boiler especially with 22 rads and are decent sizes now.



  • #6
    Wearb
    Moderators, Home & Garden Moderators Posts: 6,383 Mod ✭✭✭✭Wearb


    A bigger boiler might not improve output. It depends on what your piping is able to deliver, radiator sizing ,pump size and speed, radiators turning on and off etc. Sometimes a larger radiator will not improve output, if the pipe work to it is already maxed out.

    Your plumber will be able to advise if a larger boiler is needed or indeed if your system is even capable of utilising extra boiler output.


    The above is one of the reasons why a calculator alone might not give you proper guidance when sizing for an existing system.

    Please follow site and charter rules. "Resistance is futile"



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  • #7
    John.G
    Registered Users, Registered Users 2 Posts: 3,623 ✭✭✭John.G


    3000 FT2 = 289M2

    A better yardstick than the BER might be a heat loss indicator HLI. Its very difficult to get the relationship between HLI and BER ratings but your HLI is surely no worse than 5. So boiler power required based on this is 5*289*20 = 28900 watts, (to heat house from 0C to 20C) so a 32kw boiler should be fine but probably prudent to install a 35kw.



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