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determining boiler size

homeowner2 Member Posts: 8
I am replacing my hot water gravity fed boiler.  9 out of 9 plumbers did not conduct heat calculations to determine boiler size.  When I ask them about conducting the heat loss calculation they tell me it's not necessary based on their experience and knowledge. Some have counted and measured the radiators.    I am confused, is it absolutely necessary to perform the heat loss calculation to determine boiler size?


  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541

    Gas or oil?The smallest oil boilers are too large for most applications,for example if the smallest oil boiler is 100K,what's the point of doing a heat loss on a 1200 sq/ft house? It's not more than 100K,so why bother? With a gravity system and the old houses they are in,a heat loss is necessary
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  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited August 2011
    I Agree with Rob To A Point

    I would counter that in an oil application that a heat loss is necessary for two points. It allows me to know that I may possibly be able to down fire the boiler to it's minimal nozzle size and it will also tell me with the measurement of the heat emitters whether or not I really need to run 180 degree water temp. I may be able to set my aquastat high to a 160 degree water temp.

    If this is a gas application all of them are wrong. A heat loss is absolutely necessary for proper boiler sizing. Gas boiler are available with much lower btu outputs then oil boilers.

    Just as with the oil boiler it allows you to possibly set that water temp lower.

    Rule of thumb is, for every three degrees I can run my heating system with less than 180 degree water I can save 1% of fuel. A 20 degree drop is a tad over 6% fuel savings.

    There was an error rendering this rich post.

  • Ironman
    Ironman Member Posts: 7,376
    Only Necessary If...

    You want to size it right.

    9 out of 9 have proved they don't know how to size a boiler. Measuring the radiation is part of the process but that only shows how much the system can put out; it does not determine what the load is. If your house has had windows upgraded, insulation added, etc, then the heat load has been decreased from what the original radiation was sized for. If it was sized correctly to begin with??

    Other than the scenario that Robert mentioned above, a heat loss is mandatory. I'd find a contractor that knows how to do one correctly.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
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