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Should I replace a 52 year old boiler?

heatitup Member Posts: 1
I am considering replacing a boiler original to a 1970 built 12 one-bedroom unit apartment heated with 320 lf of finned high temperature baseboard registers. Even though the Bryant 336k BTU boiler is working fine, the side arm which supplies the domestic hot water is failing. Since the boiler is 52 years old it seemed logical to replace the boiler as well.

My questions are:
Should I keep the boiler and just replace the side arm?
What fuel efficiency could I expect with a new high efficiency system?
Should I consider two tandem boilers sized at 60% of the load for summer domestic hwh savings?
What do you think about the Mod/Con?
Any suggestions about a manufacture that has good reliability and longevity?


  • rsilvers
    rsilvers Member Posts: 182
    Need photos.

    New boilers can be 86% efficient. You can test the efficiency for the current one. I am leaving in place a 38 year old one that tested at 80% efficiency, but did redo the zoning piping to modernize it.

    Two boilers would also have savings for most of the winter if you get a Tecmar dual outdoor reset controller, so it's a question of how much extra they cost to install.
  • Jamie Hall
    Jamie Hall Member Posts: 23,567
    If you are running high temperature fin tube radiators, a mod/con won't help and won't be worth the money. High temperature radiation needs high temperatures to provide significant heat, and the efficiency gains from condensing boilers only kick in if you can get the temperatures down.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Hot_water_fan
    Hot_water_fan Member Posts: 1,906
    edited April 2022
    You'll need to figure out heat loss first. How much gas was used last year? There's a high chance that a mod-con would condense a significant percentage (depends on heat loss vs. LF of baseboard) of the heating season, so savings could be significant based on prices and total usage. A modcon can get up to 97% ish efficient. You could go with tandem boilers, but a modcon can modulate better already.
  • Jon_blaney
    Jon_blaney Member Posts: 321
    Have you talked to your accountant. There maybe tax advantages to replace or keep what you have.
  • hot_rod
    hot_rod Member Posts: 22,396
    If or when you are ready to replace I would go mod con. With 12 apartments the modulation feature, and onboard ODR is worth the cost even if it doesn't condense all season. I suspect it will condense in shoulder seasons if set up properly.

    The new Viessmanns are claiming 30-1 turn down in larger output sizes. That's a game changer for a building with loads like 12 apartments. High temperature low mass radiators benefit most from reset, according to Viessmann. No need for dual boilers with that turn down ratio.

    Check for energy rated rebates and incentives here.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Ironman
    Ironman Member Posts: 7,388
    edited April 2022
    A mod/con can offer considerable savings if it can condense a significant portion of the season. That will depend upon the building’s heat loss, the average winter temperature for your local and how the radiation is sized to the load. 

    I like the idea of two mod/cons that communicate. It gives redundancy if one fails.

    I’d also go with a properly sized indirect water heater, probably 119 gallon for 12 apts.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • wesPA
    wesPA Member Posts: 38
    I agree with the two boiler option; even though one could do decent turndown, the redundancy is nice to have and lessons the chance of the whole place going down with no heat, and most can be linked or cascaded to operate as one machine and automatically lead/lag etc..

    EBEBRATT-Ed Member Posts: 15,767
    With the way new boilers are to get another 52 years will require 3 mod con installs and probably 2 cast iron installs :)
  • Ironman
    Ironman Member Posts: 7,388
    Right now, cast iron boilers are scarce as hen’s teeth.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.