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how big is too big

Is a 150,000 BTU gas-fired steam boiler too big for a 1540 SqFt, 2 story row home with 8 baseboard and 1 coil radiators? The system is a two-pipe system, which most of the time is very noisy due to water-hammer. How much sense would it make to have the existing boiler re-piped? The boiler was installed twenty years ago by an engineer, not a heating specialist. I was told that the near-piping was not properly installed. Do you think that re-piping it would cut down on the noise? Thanks for your suggestions.


  • Eric_32
    Eric_32 Member Posts: 267
    You can't go by house measurements to size steam boiler, it has to be done measuring the radiators and or baseboard getting a total EDR and size the boiler to that. There are many sites on how to figure out EDR for different types of radiators.
  • BobC
    BobC Member Posts: 5,401
    If the near boiler piping is nt right you are probably getting wet steam, if the slope of the piping is wrong and there is water trapped in the piping that will cause water hammer when the steam comes across sitting water in the pipes.

    Make a list of all of your radiators and find one of the radiator EDR charts so you will know what EDR each one has, add them all up and that will tell you what size boiler you should have. The boiler name plate lists sq ft of steam as well as BTU's, the boiler sq ft of steam should be close to the total of all your radiators. If the boiler is too large it will be somewhat inefficient but it can still provide good quite operation. My old boiler was much to large for my system and it heated the house quietly but was not as efficient as it could have been.

    Post some pictures of the boiler and the piping around it. Get a level and make sure the steam mains are pitched so water can find it's way back to the boiler.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Jamie Hall
    Jamie Hall Member Posts: 21,111
    A boiler which is too big -- or much too big -- will waste fuel. No argument. What it will not do, though, is cause hammering. Bad piping -- near boiler or out in the system, will do it every time.

    As has been said, one of the first steps is to check the near boiler piping. Is it correct? According to the manufacturer's specs? if you can, take some pictures and we'll comment on it. Second, check all the steam pipes and any returns for proper slope. All of them, and every foot of them.

    Third, make sure the pressure on the boiler is low enough -- pound and a half, max.

    Then begin to worry about finer issues -- such as the size of the boiler, adequacy of venting, etc.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,573
    If the boiler is oil fired, or at least has a gas burner, then this can be down fired. The piping above the boiler is at least as important in making a system silent and even, so let's see some pictures.--NBC
  • ChrisJ
    ChrisJ Member Posts: 14,419
    Our house is just under 1700sqft and my boiler is 150K input. It's way too big for the house but fits the system.

    I agree with what others have said. Post some pictures of the piping around the boiler if possible.
    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
  • heatseeker1
    heatseeker1 Member Posts: 72
    Thanks to all for your excellent, straight forward advice. I will measure the rads and post a picture asap.

  • heatseeker1
    heatseeker1 Member Posts: 72
    This is the only picture I have at the moment. It only shows one side of the boiler and not the piping above the system. I'll send more as soon as possible.
  • Steamhead
    Steamhead Member Posts: 15,991
    That looks like a Dunkirk boiler- it may be have different name on it, but Dunkirk re-brands their boilers for several others.

    Whoever installed this boiler did not pipe it properly. These boilers do not tolerate improper piping, and the manual has some very specific diagrams. There are two problems I can see right away:

    1- the steam pipe leaving the boiler is bushed down from 2-1/2" to 2";

    2- the steam pipe does not rise to a 2-1/2" or larger header located 24" above the boiler's water line.

    This boiler needs to be repiped. Where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • heatseeker1
    heatseeker1 Member Posts: 72
    I live in Philadelphia. And yes you are right, this is a Dunkirk!
  • KC_Jones
    KC_Jones Member Posts: 5,409
    I just noticed something in your picture...is that a 16 ga extension cord feeding power to the transformer? If it is yikes!
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Jamie Hall
    Jamie Hall Member Posts: 21,111
    Good heavens, KC -- it surely looks like an extension cord, and it surely looks like it's feeding the transformer...

    Uh... not good, folks.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England