Installing Dampers in Existing Ductwork

Discussion in 'HVAC Heating & Cooling' started by nin28, Aug 28, 2010.

  1. nin28

    nin28 New Member

    Messages:
    45
    I have a forced air furnace that supplies pretty much all of the hot air to our utility room and office space on the 1st floor. Our bedrooms on the 2nd floor get a cool soft breeze of air. I want to install 2 dampers on the ducts feeding the 1st floor of my house so that pretty much the majority of the air goes to the 2nd floor. I realize I need to take apart the ducts to install the dampers, however, I have never done this before. Below of two pictures of the pieces I want to take apart and install the dampers. I'm sure I could eventually get them apart, but I need advice and how I could do this in the best/easiest possible way and how to get them back together. Thank you.

    [​IMG]

    [​IMG]
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,820
    Location:
    New England
    If they're what I think they are, those metal bands will slide off. Straighten out the tabs at each end, then try to slide them off. If they are what I think they are, there's a bent edge on the duct, and the band wraps around and holds the two pieces together.
  3. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    The first pic connection is what they call slip and drive. The face you see appears to be the drive side. Straighten out the bent ends and tap it off with a hammer. the other side is the slip side. These can be put back together fairly easy if you do not damage them to much. Once you take off the drive you will get the hang of how it is attached. The long attachment side which you did not ask about is probably a pittsburg lock of which is a little harder to get apart. Take a look at the attached web page for a better explaination. http://www.marstaninc.com/rec_sheet_metal.html
  4. nin28

    nin28 New Member

    Messages:
    45
    Thank you for the information. Upon contemplating the issue that I have, I'm not sure if simply putting dampers on both these ducts with supply enough heat to our 2nd floor. I'm now considering rerouting the ductwork. There are basically 3 ducts supplying all the heat to the front of our house. One of the two 6"x8" ducts I pictured above provides heat to only the utility room (100 sq ft), which has two registers. The other 6"x8" duct provides heat to our foyer (48 sq ft) with a single register and the office (120 sq ft) with two registers. The 3rd duct is 9"x10" and splits with one run providing heat (if you can call it that) to my daughter's room (120 sq ft) above the utility room and the other run provides heat (insert joke here) to my sons room (72 sq ft) and our master bedroom(144 sq ft). As I mentioned above, the 1st floor gets all the heat and the 2nd floor practically none. I'm wondering about strategies to redo the duct work. During the winter we would have the registers mostly closed on the 1st floor so the heat would go to the 2nd floor. I was thinking of removing the duct run to my daughter's room and connecting the register to the smaller 6"x8" duct that feeds the utility room. Also, I would connect the two registers that feed the master bedroom and the one register that feeds my son's room to the 6"x8" that feeds the office and foyer. This would essentially eliminate the largest duct that provides very little heat to the 2nd floor. What do guys think of this? Thanks for any help with this issue.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,820
    Location:
    New England
    Regardless of the duct size, if the cold air return ducts aren't well designed, you may not get heat where you want it. If you don't have a path for air to return to the furnace to get reheated, it's sort of like trying to blow up an already full balloon. If you don't have a return duct in the room(s) upstairs, and there's not enough leak under the door or some other pathway for the air to get out, you can't blow the hot air in. Often, there's a cold air return in the hallway. That might have worked before carpeting, and other stuff might have taken up the gap on the bottom of the doorways, but not now. Depending on the door, you might be able to cut some off to provide a path. Or, install a grill on the wall (or door) to the hall (one on each side), or, (this could get quite messy) extend the return duct to the rooms. You might be able to increase the fan speed, but that may exceed the capacity of the ducts, or make them noisier. Booster fans for the cold areas can be installed in the ductwork to increase flow. Shutting the register grills isn't as effective as a properly located damper, but can work. Leaving the doors open makes return duct placement moot. Setting the furnace fan to run continuously can help.
  6. nin28

    nin28 New Member

    Messages:
    45
    The return is in main hallway and we keep all the bedroom doors open because we have infants, so I don't think what you explained is the issue we're having. So you don't think its the size of the duct supplying the 2nd floor is the issue and if I install the dampers as I explained originally along with booster fans that may solve the issue? And finally, you don't think I should run new duct work? Thanks.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,285
    Location:
    Cave Creek, Arizona
    Normally, heat to the upper levels is NOT a problem. The common problem is that there is too much heat there because heat from the lower level rises upstairs, unless you have a sealed stairway so the heat cannot circulate up there.
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,820
    Location:
    New England
    You'd need an analysis of the house, the heating system including the duct sizes to determine if changing the duct size would help. The amount of heat you can carry in a certain sized duct at a certain air temperature with a specific fan speed can be determined. Then, the house analysis determines how much heat is actually needed and if the source, air velocity, and duct sizes are adequate. WAGs can get expensive. What often happened during construction, or building settlement, is that some of the seams may have come apart on the duct(s), and you are putting air into the wall cavity. If it is an interior wall, it might not be as bad as if it were an outside wall. Air likes to go on the path with the least resistance, so since the ducts to the first floor are usually shorter, they get more air. But, if your ducts are sized properly, those might end up smaller, while the second floor's ducts are larger so the relative resistance is the same (assuming equal areas and load). You can change the relative resistance by putting dampers in, but if there a lots of leaks, and the sizes, both to the downstairs and upstairs aren't adequate for the required flow to distribute the required heat, it won't help much. You might be able to increase the fan speed, but there are limits. Too high and things get noisey, turbulance and rumblings, and the air temp decreases because the air passes the heat exchanger faster, cooling things off and that could create other problems with longevity, too. Plus, at faster air speeds, like a summer breeze, you feel cooler. It could also be that the return ducts, regardless of where they are, are too small, starving the whole system for airflow. Remember, with the supply and returns, it is sort of a closed system...you can't efficiently fill the system to capacity if it is starved for air on the return.
  9. nin28

    nin28 New Member

    Messages:
    45
    Thanks Jim for the thorough explanation. I think you are probably on to something in regards to the returns. The return on the 2nd floor is tiny compared to the sizes of the returns on the 1st floor. We're having an HVAC guy come here on Monday to check it out. From the way the returns are run I think we could pretty easily run a larger return to the 2nd floor. I'll let you know what the guy determines. Thanks for the help, once again.
  10. nin28

    nin28 New Member

    Messages:
    45
    An update before the HVAC guy gets here on Monday. I partially sealed up the first floor furnace intakes to see if it would affect the amount of hot air going to the 2nd floor. No noticeable improvement unfortunately.
  11. nin28

    nin28 New Member

    Messages:
    45
    Had a couple HVAC guys out here and they suggested zoning my house by putting in electronic dampers in. The house will be separated into 3 zone with 3 thermostats. Does anyone have any experience with this type of forced air configuration and has it been successful? Thank you.
  12. Estrogen Hostage

    Estrogen Hostage New Member

    Messages:
    18
    Location:
    NE KS
    How old is the house and where are you located?

    In my experience old houses had inadequate ductwork to begin with, especially if they were originally set up for heat only. Adding dampers to make up for inadequate ductwork is going to be an expensive fix that might create as many problems as it fixes. I had similar issues in my old house - and anything that tried to fix it would just destroy the efficiency of the system. I actually found that the best solution for me was to install a small return vent and supply vent to the basement to dump air and make up for inadequate ductwork. Mine was so bad that we had to turn the pressure down on the heater because it was tripping the high temp limit switch due to not enough air flow. The AC was the same situation - a 2.5 ton house could barely keep cool a 1250 sq foot house with R19 walls.


    My suggestion would be to live with it the way it is and supplement with baseboard heat or a window unit or even a few ceiling fans to keep air moving. It might be worth looking at when you replace the system, but I bet the electronic damper system will cost nearly what better ductwork will.


    BTW - I am not an AC guy.
  13. SteveW

    SteveW DIY Senior Member

    Messages:
    1,052
    Location:
    Omaha, NE
    Not sure if this is relevant or not, but I saw on This Old House a couple years ago a system called "My Temp," which is designed to easily retrofit air-bag type dampers into residential ducts. Each room then gets a wireless thermostat which feeds info to a central controller that regulates air flow to each room. Supposed to be a lot easier and cheaper to put in compared to conventional mechanical servo dampers. It seemed like a pretty clever idea at the time.
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