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Two boilers instead of one?

wam525
wam525 Member Posts: 18
Our old oil-fired steam boiler died, and one contractor suggested that, since the large boiler we have may not be available for many many months, we might consider putting two available smaller boilers (each with half the capacity) in parallel. Does this sound reasonable, even if the cost were not that much more?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 18,941
    Has anyone checked what size boiler you really need? While there are times when the old boiler is the right size, it's also unfortunately common that it is bigger than is needed. Replacing like for like is not always the best choice.

    Fortunately, with steam, its really easy to do: add up all the connected radiation in the structure, and compare that to the EDR rating of the boiler. The size you need is that, or slightly less. Don't oversize.

    Getting two boilers to play nice together is certainly possible -- but it isn't quite as simple as just putting in two boilers and hooking up some pipes.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    In_New_Englandmattmia2EdTheHeaterMan
  • ethicalpaul
    ethicalpaul Member Posts: 3,739
    edited May 19
    Definitely have your current sq ft of steam (EDR) of your radiators measured before you even think of ordering a boiler.

    I wouldn't even think of trying to run two boilers in a home, you're just asking for trouble and a lot more expense. That advice would have me looking for a new steam contractor.
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,002
    With steam two boilers are more expensive and the piping can be tricky unless the installer is very good you could have problems controlling the water line. You need a lot more controls to twin two steam boilers together successfully which is expensive.

    I would avoid it unless the building is quite large
    ethicalpaul
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 930
    Depending on the system, using two boilers can be much more efficient if the system is properly set up to take advantage of a variable input steam heating plant. I just installed a twin heating plant at my church 2 years ago. Its great to see the heating plant running during the week when much of the building is in setback with only a single 345,000 input boiler heating 15,000 sq ft right down to -5F. However, as others have said, the designer really needs to know what they are doing. These two 345,00 input steam boiler along with a 150,000 input hot water boiler replaced a 2,100,000 input steamer. .
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  • wam525
    wam525 Member Posts: 18
    Thanks, guys. All good comments. To me, two in parallel sound pretty tricky to set up especially if not absolutely needed. The total radiator sq footage is around 900, so on the higher end of residential.
  • Steamhead
    Steamhead Member Posts: 15,334
    Look at the Weil-McLain SGO-9 or Slant/Fin TR-60.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    EdTheHeaterMan
  • mattmia2
    mattmia2 Member Posts: 5,525
    If it were hot water i'd say it gives you redundancy and better match to load on milder days but like others said, steam is a lot harder to do properly.
  • SteamingatMohawk
    SteamingatMohawk Member Posts: 740
    To better inform the HHers, what are the ratings on the boiler nameplate, including the model number? Compare that to your EDR and go from there.

    Use the KISS method, don't make it unnecessarily complicated. Some day you will sell the building.

  • The Steam Whisperer
    The Steam Whisperer Member Posts: 930
    Could maybe even due a single 380.. when the castings become available.
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  • mattmia2
    mattmia2 Member Posts: 5,525
    A discussion about how well the EDR matches the building and what happens if we make the boiler a little undersized, can we still make it heat evenly might be warranted here too.
  • ChrisJ
    ChrisJ Member Posts: 12,851
    mattmia2 said:

    A discussion about how well the EDR matches the building and what happens if we make the boiler a little undersized, can we still make it heat evenly might be warranted here too.



    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    ethicalpaul
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 930
    With two pipe steam, that is certainly something to look at since it is so easy to "virtually downsize" the existing radiators with orifice plates. For buildings built after around 1905, it seems that the radiation is usually about 60% oversized for the original building load. If the building has had thermal upgrades that number can grow significantly.
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