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Slant Fin Series 310

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I can't find information on our Slant Fin Series 310 boiler in our house we bought last year. The HVAC folks who assessed it said they had never seen such a big boiler in a non-commercial setting and would take two boilers to replace it due to the number of radiators. The house is vintage 1910 and about 4500 sq ft. The boiler works well but must be very inefficient. Can anyone tell me about how old it might be? Would parts be available somewhere if needed? I have attached a picture of the spec plate.

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  • bburd
    bburd Member Posts: 926
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    ”Two boilers to replace it”?  Nonsense.
    These people must only work on smaller or newer houses.

    Bburd
  • hybridescapist
    hybridescapist Member Posts: 4
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    Pretty sure they work on old big houses and some commercial applications. Could be I was only getting what a specific mfg could do for residential. They seemed pretty amazed by 462 BTU/Hr in a residence. My only point of reference is our 1600 sq ft Sears kit house that had a 165 BTU/hr boiler.
  • bburd
    bburd Member Posts: 926
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    Many steam boilers are oversized. They should be sized according to the connected radiation load, usually calculated as “square feet of steam EDR”, but many contractors don’t bother; they just replace an existing boiler with the same size or larger. We can help you calculate this, it’s not difficult.

    Bburd
  • hybridescapist
    hybridescapist Member Posts: 4
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    The contractor counted up all the radiator fins and dimensions. There are radiators on all four floors. If we ever need replacement we'll get second and third opinions. It is hot water, not steam, but I expect the methods are similar.
  • bburd
    bburd Member Posts: 926
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    Ah, hot water! Surprisingly, the sizing method is quite different. A replacement hot water boiler should be sized according to the current heat loss of the house. Most older homes have been upgraded with better windows, perhaps attic and/or wall insulation, since they were built.

    The difference in method is because with a hot water system, reducing boiler capacity will reduce average water temperature evenly throughout the system. With steam, reducing boiler capacity below what the radiation can condense is likely to cause some radiators to heat fully while others will not, leading to unbalanced heating.

    Bburd
    hybridescapist
  • hybridescapist
    hybridescapist Member Posts: 4
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    bburd, thanks for the clarifications. This site is extremely useful. Glad I stumbled on it. The boiler plate seems to indicate that it could be used for either hot water or steam. Ours is definitely hot water. We learned that the outside walls of this house has no airspace for insulation. It is three layers of brick with plaster directly on the inner layer. I didn't believe it until the electricians showed me. Made it very hard for them to hide any wiring on an outside wall. Also, the hot water heat had to be added after the house was built, since every room has a now inoperable fireplace. That might explain the odd radiator locations. Sometimes under windows, often not.
  • bburd
    bburd Member Posts: 926
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    @hybridescapist if you get a heat loss calculation done, you will want to point out that unusual exterior wall construction. It’s probably not obvious on the surface, and makes a big difference in the heat loss of the house.

    Bburd