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Sizing a new boiler

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John L
John L Member Posts: 118
in THE MAIN WALL
We dont do many boilers, mostly hot water,we use the sq. ft of radiation to size the boiler, where are we going wrong when we use the sq. ft of radiation when we are dealing with hot water boilers? All help appreciated.

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  • sidney r. bray
    sidney r. bray Member Posts: 26
    Sizing a new boiler/boiler leak

    My HE 5 Weil McLain (1987 model)has a leak in one of the cast iron sections. According to them I would be better off replacing the whole block or else replacing the boiler..since it will take a minimum of three weeks to get the block, I'm leaning towards a new boiler. Tech support person where I bought one of my three baseboard cast iron radiators (the balance are the free standing older tube or column type radiators) suggested doing a Manual J Heat Loss to size a new unit, that if I use the sq.ft. of radiation, pipe sizes, etc method you will almost guarantee to oversize the new boiler. Who's right? Also, can the hairline crack be repaired with a sealer, we tried a product called Sealmaster to no avail, is there another product that might work? I have a hot water system not steam. Weil McLain person suggested Fels Napa soap has been used successfully by some contractors to seal cast iron leaks in boilers. Anyone have any suggestions? I'm loosing about a drop a second when the boiler is not running, less than that when it is cycling.
  • Empire_2
    Empire_2 Member Posts: 2,340
    Depending on how much

    If you have 200m in radiators and the house man J's out to 100m or so, unfortunatly you have to size the equipment according to what you have as far as convectors go. Even though an undersized boiler is what you need you will experience lo return temps and cool radiators. Longer run time and possible thermal shock could result. There are alot more particulars that need to be known, but that is my opinion.
  • Jim Dawson
    Jim Dawson Member Posts: 6
    Hair line leak

    Here's a tip that most people overlook. The radiator system in your home uses about the same temperature as an automotive system.Infact I think the auto rads can run a little hotter,I have used automotive stop leak.It works great and plugs the hair line up.
  • Ron Schroeder
    Ron Schroeder Member Posts: 995


    Hi Sidney,

    If it is steam, you need to size to the radiant. If it is hot water you need to size to the house's heat loss.
  • Big Ed
    Big Ed Member Posts: 1,117
    Agree .....

    ......but like to add,you must take in account if the boiler is being used for domestic hot water ,the hot water load could be larger then the heat load.The boiler needs to be sized to the larger load.
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