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Two vent dampers for efficiency?

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Mark Oppedahl
Mark Oppedahl Member Posts: 14
in THE MAIN WALL
need to insulate the near-boiler piping yet so it'll definitely get better when that's done.

Comments

  • Mark Oppedahl
    Mark Oppedahl Member Posts: 14
    Two dampers on steam boiler?

    We've installed a new steam boiler in the house and per specs it has a draft diverter on the stack with a vent damper above it. Old boiler had no damper so it's great not to have the warm basement air sucked up the chimney between cycles. But now when the damper's closed, the residual heat of the boiler vents to the room, and it gets w-a-r-m. Wouldn't it be more efficient to trap the heat in the boiler until the next cycle? Don't want to move the damper below the diverter because the air'll go up the chimney again. Anybody ever install two dampers, one above the diverter and one below?

    -Mark O
  • Weezbo
    Weezbo Member Posts: 6,231
    induced draft?

  • Mark Oppedahl
    Mark Oppedahl Member Posts: 14
    Not induced,

    natural draft. Hydrotherm VGA-400 if that's helpful.
  • Gary Fereday
    Gary Fereday Member Posts: 427
    Jury Rigged ?

    I wonder what the local authority would say? I'd bet he have a fit!
    However, if you did that with electric motorized vent dampers, and had them wired in series with the T/S turning on one then the other, and proving both open to the fuel supply, Why not? It might be a least expensive way to control the heat after the boiler turns off. Liability here is a concern!
  • Mitch_6
    Mitch_6 Member Posts: 549
    Second vent damper.

    If it was a good idea to install the vent damper on the breach before the vent hood I believe the manufacturer's would have done so in the first place.

    I believe the heat will want to go somewhere like roll out at the base

    I assume this boiler is standard cast iron steam boiler.

    I would not want to hang my ticket on doing something like that. Seems we get into enough trouble doing what the manufacture says.

    Mitch S.
  • MIKE6
    MIKE6 Member Posts: 102
    2 dampers thats a no no

    A damper before the diverter is against code,not in the installation manual and dangerous.One reason is if the gas valve was to hangup in the open position and the 2 dampers closed the flames would come out from the bottom of the boiler.If combustibles are near a fire will start.Even though there is a flame rool out switch,the flame may not roll out near the switch. Back to the drawing board!
  • MIKE6
    MIKE6 Member Posts: 102
    2 dampers thats a no no

    A damper before the diverter is against code,not in the installation manual and dangerous.One reason is if the gas valve was to hangup in the open position and the 2 dampers closed the flames would come out from the bottom of the boiler.If combustibles are near a fire will start.Even though there is a flame rool out switch,the flame may not roll out near the switch. Back to the drawing board!
  • Unknown
    Unknown
    No!

    You don't want to install the vent damper below the draft hood. The blocked vent switch is below the vent damper, usually on the draft diverter or in close proximity to protect against combustion byproducts entering the living space in the event of either a flue blockage or the damper not opening and the burner firing. Can that really happen? You bet your bippee it can and all it takes is a diligent person with creative wiring tehniques trying to wire in an indirect heater, low water cutoff, power venter or draft inducer by cutting into the factory wiring harness.

    Adding a second vent damper introduces a liability issue into the scenario. Unless they are wiring in series so that one has to prove it is open before the second can open can allow the possibilty of the boiler still firing even though one has not opened. Besides, I really don't think you will have that much to gain. The damper only adds a couple of percentage points to efficiency and the second one will only be a fraction of that. Hope this helps.

    Glenn Stanton

    Manager of Training

    Burnham Hydronics

    U.S. Boiler Co., Inc.
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    some more thoughts

    if the inducer is not running and the burners light it will roll out... no different than two dampers.
    I too have thought about this. I believe the chief reason the damper is above the draft hood is that it improves the Afue rating because heat backing out of the drafthood is considered "usable" by afue standards. I have been in some "cooking" boiler rooms just full of the heat from closed stack dampers on draft hood boilers. Most of this is just wasted up the stack or ventilated outdoors and can wreak havoc on the life of controls and equipment.

    Maybe its time the manufacturers look into this as a way of improving "real" efficiency, and still keeping equipment rather simple.

    boilerpro
  • bob young
    bob young Member Posts: 2,177
    life &

    amazing how many people with money saving suicide schemes post on this forum. a lot of people do not have the proper respect for gas & carbon monoxide. this stuff can actually be lethal to families
  • Boilerpro_3
    Boilerpro_3 Member Posts: 1,231
    Most heat will stay in the boiler

    Hot air rises, so it cannot fall out the bottom of the boiler, unless air is pushed in the top. One of the unique drafthood designs on the market is the older Lochinvar residential boiler. The draft hood relief opening is below the heat exchanger, so when the stack damper is closed, the heat is trapped in the boiler.

    Boilerpro
  • Timco
    Timco Member Posts: 3,040


    Is that not a great use of this site?? To ASK before action? Great ideas are born and lives saved by asking....not just acting.

    T
    Just a guy running some pipes.
  • Mark Oppedahl
    Mark Oppedahl Member Posts: 14
    Thanks...

    for the info guys. Safety first obviously -- a half a percent of efficiency isn't worth the risk. As long as the heat's somewhere in the house, even in the basement, it's better than up the chimney like the old boiler with a crack above the waterline and no damper at all. -MarkO
  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    Mark, are there any other unwanted heat sources in there

    such as uninsulated pipes? If so, fixing them would help.

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  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    Sometimes it doesn't even take that much

    to cause problems. Read this one:

    http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=33429&mc=10

    In this case, the blocked vent (spill) and roll-out switches were effectively bypassed. If a second damper was on this boiler it would have rolled out, with disastrous results.

    Since you have a steam system, the chimney was likely built for coal firing. Coal boilers needed a lot of draft, but oil or gas-fired ones do not. A good coal-designed chimney can draft so strongly that it pulls much heat out of the boiler on the off cycle, so the damper between the draft hood and the chimney is quite effective.

    Glenn, has anyone gotten around to testing damper effectivenenss when a boiler is installed on one of these old chimneys?

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