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unico supply ducts (leakage)

All of the supply duct for the unico is in the basement. It was built with the square metal sheets that fit together to make a round section then each section was screwed together. The installer did use the silver metal tape on each section except for the graduated elbows. The elbows (which I have six) have the air leakage. Each elbow has several sections that you can twist to go in diferent directions other than a 90. Some one on this string mentioned mastick. Can someone explain in more detail of how the mastick is used. I asume it is a glue that seals the connections?

Comments

  • scott w.
    scott w. Member Posts: 207
    unico supply duct (leakage)

    Just had a 5 ton unico system installed in a fairly large two story house. The supply was installed with a long circular, 9 inch main supply duct in basement with six corner bends.
    The supply duct is wrapped with insulation. I noticed a couple of places the insulation was not taped together and happened to stick my hand in between the insulation and the piping and noticed a good deal of air flow. It seems as though none of the corner joints of the bends of the pipe were taped.
    Since the unico is a high velocity system how critical is this air loss in the basement to the rooms on the second floor which have the longest runs? Shouldn't the installer come back to remedy this issue?
  • scott w.
    scott w. Member Posts: 207
    unico supply duct (leakage)

    Just had a 5 ton unico system installed in a fairly large two story house. The supply was installed with a long circular, 9 inch main supply duct in basement with six corner bends.
    The supply duct is wrapped with insulation. I noticed a couple of places the insulation was not taped together and happened to stick my hand in between the insulation and the piping and noticed a good deal of air flow. Upon inspection none of the corner joints of the bends of the pipe were taped.
    Since the unico is a high velocity system how critical is this air loss in the basement supply duct to the rooms on the second floor which have the longest runs? Shouldn't the installer come back to remedy this issue? Is the air leakage something to be concerned about?
    This is a great place for a homeowner to learn quite alot. Thanks much for any help on this.
  • don_182
    don_182 Member Posts: 69
    Yes

    all duct joints should be seal.It helps keep the pressure in the home either from becoming a negative or a positive.
    Now if your ducts are inside the envelope then it not much
    of a issue.

    We try to offer duct sealing as a option and used to add it
    in on our quote untill,we lost many of projects because we were higher then most.

    And even now no matter how hard we try to explain to the customer how important it is to seal the duct..they still put the carriage in front of the horse.

  • Empire_2
    Empire_2 Member Posts: 2,343
    Don I agree.

    Although it is an additional cost, all home owners q: and concerns should be addressed and rectified. My main concern is the total static reading on the trunk line and the output of the actual outlets. There is a set, manufacturers specifications of what should be available. ALL duct will leak, unless sealed. I would approach this as a matter of curiosity and is it normal and be reassured that there will be no problems in the future. Without knowing the layout of your structure, We can only guess what the contractors intentions were and his acceptable performance of the unit as a whole. Just remember that we are only human and something might have been overlooked. Don't bring out the gun's cause it is not necessary at this time. A friendly call can work wonders in a contractors eyes.

    Mike T.

    Just as a note,....Once,..OK twice in my career I did service calls on Commercial jobs and forgot to turn the disconnect back on. I know, Duhhhh, but it happens. Got a call back and both calls, all OK, but one customer was an **** just like me and the other was very nice and I was the only ****. Signed tail between my legs.;-)

    Mike T.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Personally, I am Bullish on Duct Sealing....

    You know the older high velocity systems, the dual duct and induction systems installed in the 1950's and 1960's? They had that red brush-on sealant and were practically airtight. I tested several for integrity and they passed with less than 1% leakage. The reason they sealed so well was not energy, it was relatively cheap back then. The reason I was told was noise. At 4-5,000 FPM the ducts would whistle you can imagine.

    Today it is energy. In order to recoup the lost percentage of air (and it is greater at higher pressure) you would have to spend horsepower by a power of 3. (10% leakage? 30% HP in rough terms.)

    I would seal the living s*** out of any duct in that category with a good brush-on mastic or Hardcast tape and activator. I feel strongly about this... with a Unico type system, a good leak could be wasting an outlet... where is the control in that? Just because it is in the building envelope does not mean it is well spent.

    My $0.02

    Brad
  • Mark_46
    Mark_46 Member Posts: 312
    Scott

    I too am in the final throws of a Unico High Velocity system install. On my first floor air handler a 90 elbow comes off the air handler to a T (which I dont like. I would have preferred a Y, less pressure drop, but I digress). At that T there is significant leakage. I will without doubt ask the installer to correct this. I think you should do the same.

    When that air handler is on, the insulation jacket around the plenum puffs out! I know the joint at the T is the source. It was fabricated by hand using stock lengths of duct, not manufactured elbows with integral rubber seals, etc. I can understand errors, we all make them. But it must be corrected.
  • don_182
    don_182 Member Posts: 69
    Bullish

    can be a good thing.Hello Brad. When I mention that is was no big issue maybe I should have said no big deal with pulling a neg/pos on the building envelope.

    As for getting the air where it need to be and to balance out the system then you're correct, it should be seal as well.

    Heck.. it use to be no need to insulate the ductwork when it was inside the building envelope but that too has change.



  • Brad White_87
    Brad White_87 Member Posts: 24
    Hi Don

    No criticism was intended by the way; just my view... Insulation -for cooling we agree especially in humid climates. If heating only, I would take absolute sealing before I go for insulation. Not just the sequence of construction but if I hypothetically could choose only one...

    Ever pressure test a duct system? You would be surprised how (poorly) most perform.
  • jim lockard
    jim lockard Member Posts: 1,059
    Air leaks

    I find alot of homes with air leaks to the point where the home will not heat or cool. I recently had to let a duct crew go, because they could not understand that I wanted an airtight duct system. I do not beleive I am asking to much to tape and seal the duct system. Best Wishes J.Lockard
  • don_182
    don_182 Member Posts: 69
    None taken Brad.

    Back in the day when we did duct leakage test we found the
    biggest leaks in the distribution system to be at the airhandler.

    Door panels,where the copper came thru the door panels and
    underneath where the pleum attached to the ah.




  • Brad White_87
    Brad White_87 Member Posts: 24
    That's right, Don!

    How many times did we have to tape off or cap off the AHU (where pressure differentials hence leakage are greatest) just to see what the "ductwork" leakage rate was.

    Commercial double-wall units these days do perform very well although occasionally one of a reliable line proves to be leaker than it's production counterparts.

    Another trivia tid-bit: Our Massachusetts State Energy Code states specifically that duct tape shall not be used to seal ducts. (We know how it dries up and falls off). Imagine- duct tape outlawed. Only here in Mass.

    Oh- as one sage pointed out: Duct tape is like The Force; it has a Dark Side, a Light Side and holds the Universe together :)
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    I'm intimately familiar only with Unico, but have studied literature from two other Hi-V mfgrs. All make a BIG DEAL about duct sealing. Proper operation, economy and noise issues are all mentioned regarding duct sealing. Kind of hard for me to see good duct sealing as an "extra-cost option" with these systems.

    From the components and instructions provided by Unico, you can tell that they're serious about duct sealing.

    I did though notice something curious (to me) about the scrim core (sound attenuating) tubing. The inner scrim core is NOT air tight--fairly easy to blow through--but the outer foil wrapping is airtight. Seal the ends nicely with the tape rings supplied and also tape any "accidents" in the outer foil.

    I was thoroughly impressed with the quality and service from Spiral Manufacturing. If you need custom components, the catalog is EXCEPTIONALLY WELL DONE! As long as you follow the wonderful illustrations of nearly any conceivable component, your chance of specifying them incorrectly is nearly impossible. My order arrived within 10 days of my final approval.

    The component near the back of the photo (just in front of the small piece of spiral pipe) is a custom rectangular to round + offset for connection to the Unico blower module. Perfect to spec.
  • Plumdog_2
    Plumdog_2 Member Posts: 873
    International Energy Code

    as part of the IMC and IPC and IBC, we have the IEC; and it mandates that ducts be sealed. This must be done with approved mastic or tape depending on the application, and the finished system must meet a certain minimum standard of leakage. (duct tape is verboten; a fire hazard). This requirement is not enforced in all counties or municipalities as of yet; but I think it should be. For one thing it seperates the wheat from the chaf. If you can't be bothered with sealing ducts, you probably won't bother with proper hangers and supports either; and your branch lines will come apart in short order.
  • Mark_46
    Mark_46 Member Posts: 312
    Mike

    Interesting.

    These look very smilar to what my installer used but then again most duct work looks similar :o).

    But the main plenum material in my system also has (the best i can describe) impregnated dual neoprene seals at the joints too. Nice touch I thought. Are these the same?
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    I've never seen such connections, but that doesn't mean too much... I joined these using screws and duct mastic, then covered with aluminum tape. Do note that these tees, elbows, etc. are welded at all joints. Leaks are impossible in the fittings themselves.

    I noticed in your previous message that you were somewhat concerned that the first fitting after the air handler is a tee. Does the main plenum form a loop? If so, such is the perfect configuration for a high-velocity system as that makes a "pressure-balanced loop". Every branch will have the EXACT same pressure available at its connection to the plenum. This arrangement GREATLY simplifies the engineering and should be used whenever possible. If memory serves, the initial tee is ideally located about 3' from the air handler with NO takeoffs made before the tee or within about 3' in either direction.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    \"Loop Ducts\"

    are a great way to minimize balancing issue. One cannot say that the pressures will be exactly the same all the way around, but the gradient from maximum (near the air handler discharge) to the minimum (furthest port in either direction) is indeed small.

    The initial "tee" (or better, a "wye" with 45 degree elbows) has a minimum distance from the AHU discharge due to what is known as "system effect". The fact that the air is leaving an AHU fan via an imperfect profile requires that the air velocity become more uniform before hitting that first elbow, tee, split or other branch. Otherwise the best "laboratory" measurements will be off by a factor of 3.0 or more. Huge.

    Sort of like tripping a horse out of the starting gate at Churchill Downs and still expecting the horse to finish reasonably.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
    \"Lindab\" fittings

    are at least one brand that has the dual neoprene ring seals. Very nice system. I use them for dryer exhaust because of the friction fit. Easy to disassemble for cleaning. Look them up!
  • Mark_46
    Mark_46 Member Posts: 312
    Mike

    Ya, I thought the first T in my plenum was handmade but it is in fact a manufactured piece. Phwew, that was a relief. I thought the installer fabricated it but I didnt actually see it go in before the insulation jacket went on. So I thought it was done with tin snips, by hand and fabricated on site. It wasnt, my misunderstanding. So that T is not a potential leak source as I originally imagined.

    To your question about the plenum, no it does not form a loop. But what your describing makes a lot of sense! This plenum is more U shaped. Yes, this T is about 3 feet from the AH. From the A.H. it rises vertically about 12 inches to a 90, extends about 24 inches horizontally and goes into the T. My first mini duct take off I would guess is about 3-4 feet after the T in both directions. But I would really need to measure, thats just a guess. This particular installer specializes in Hi-V so I would think they would have that stuff down pat.
  • Mark_46
    Mark_46 Member Posts: 312
    Brad

    Ya, that could be the manufacturer but I dont know for sure. what I do know is I was pleasantly surprised to see a nice detail like that. I was expecting conventional round duct with the slip fit connections that eventually get screwed together, etc.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    Exactly

    Sorry for my hyperbole Brad.

    I will say though that it's exact enough that the convolutions (or lack of such) in a 10' "standard" run will have more effect once the system is fully pressurized.

    I have pressure-balanced loops in my irrigation systems, low-voltage lighting systems and domestic water systems. When in "show off" mode I'll have a person put their hand under the stream of a lav faucet with both hot and cold full open. Then I'll flush FOUR toilets. No perceptible change in temperature even though the flow diminishes a touch... "How'd you do that?" "Simple" I say...

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    Sounds to me like your installer has done a good job and knows his stuff. The only thing I don't understand is noticeable air leaks from the plenum.
  • Mark_46
    Mark_46 Member Posts: 312
    Mike

    During the follow up visit, I mentioned the noticable leaks and insisted (trying not to be to crazy about it) they take anothet look. Turns out one of the joints didnt get taped! One of the crew probably just forgot. No biggie, it was an easy fix too. Although, i stil think there are some leaks. Kind of what Brad was mentioning, might not get these things to seal 100%.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928


    There will be air leaks--after all this is neither screwed pipe nor sweated copper...

    The joints you describe sound like those used in the Vitodens venting BUT such is operating at significantly lower pressure.

    I seal my traditional A/C systems to the point that the air handler is the weak link...then I start sealing it...

    Perhaps I put too much faith in aluminum tape.
  • Mark_46
    Mark_46 Member Posts: 312
    Sealing

    Mike, I wish i could go around the plenums and 'touch-up' any small leaks. but with the insulation jacket on already and the miniduct take-offs installed right over the jackets I cant get to anything without cutting the insulation jackets.
This discussion has been closed.