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Why is one heating duct producing more heat than....?

mike1 Member Posts: 21
Hello guys, this is a 60 year old house with a Gas central heating system. Main issue I think with this house is the uneven distribution of heat in the vents as only one room on each floor has a lot of heat while the other room's vents do not put out same amount of heat. The ducting is a like a tree trunk with different branches and some branches are not putting out the same amount of heat as the main one which simply baffles me and to which no one, not even my friends who do boiler installation and repairs can give me an explanation for this.

What possible reason could there be for a heating system to have more heat in only one duct and much lower heat in others, why couldn't they apply the same amount of heat to all ducts please?


  • Jamie Hall
    Jamie Hall Member Posts: 18,935
    edited January 2018
    Air is not different from steam or water that way -- it's lazy, and will go the easiest way. Even relatively small differences in duct length and geometry can make a big difference.

    If the cooler ducts are taking off at 90, and the warmer straight ahead... as I say, the stuff is lazy.

    And the answer is control dampers.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mike1
    mike1 Member Posts: 21
    Yeah, I don;t think they even put dampers in these ducts as I have never noticed any damper levers, will look more closely this time and take some pics in a few hours.
  • hot_rod
    hot_rod Member Posts: 16,304

    Iin commercial buildings there are specific contractors that balance the air side HVAC. Some of the progressive HVAC residential shops have hoods to measure and balance.
    But you already know where you need more or less.

    You can buy adjustable grills for most any duct opening.

    Or cardboard :)

    The ducting needs to be sized properly to allow adjusting so you do not create problems back at the furnace.

    Insulating any exposed duct work can make a difference also.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,330
    I picked up one of these a while back. http://www.testequipmentdepot.com/aab/anemometers/bluetooth-airflow-environmental-anemometer-abm-200.htm?ref=gbase&gclid=EAIaIQobChMIwK38_KfJ2AIVQrbACh3THAeNEAQYASABEgIf__D_BwE
    It is certainly not as good as an air hood but works great for estimating flow and spot checking air balance.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mike1
    mike1 Member Posts: 21
    Sorry it took so long for me to get the pics and it's not easy to take the pics in the boiler room. This is a Thatcher Gas Fired heating system. First pic shows that at the top of the heater there is the main trunk then 3 main branches going in different directions [like a T].


    2nd pic shows those 2 wing nuts, would those be the dampers?


    If yes, I am also seeing wing nuts on one of the other branches but all of those wing nuts are located at least a few feet away from the base of the trunk.
  • Fredm
    Fredm Member Posts: 4
    How does the cool air get back to the furnace? Unless you have a return grill in each room, you have to provide a way for the cooler floor level air to get back home.
    Typically in my part of the world there is a central return air pick up instead of a return air opening per room. That means that in order to get back home the air has to squeeze under the door. Inadequate undercut results in the phenomenon you describe.
    A rule of thumb suggests that you need a 1" undercut between the top of the present floor covering and the bottom edge of the door.
    Oh and by the way, leaving the door ajar is not the solution either.
    JUGHNE Member Posts: 9,761
    Does your heat come out of high wall registers that are located on inside walls?
    EBEBRATT-Ed Member Posts: 11,998
    Yes, those wing nuts control dampers. That style of ductwork is probably from the 50s...they called them "railroad fittings"

    You can probably do some balancing. Start with all the dampers wide open. Do this on a cold day when the system is operational. Make small adjustments and give the rooms several hours or a day to settle out. Start by closing the rooms that overheat. If you have several rooms that are cold you may have to restrict the airflow into the room that has the thermostat to get the furnace to run longer.

    and yes. as @Fred mentioned returns are as important as supplies