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Flexible Duct Adapter Puzzlement

Hi All!
In our home, we have a horizontally mounted High Velocity HV70-BU air handler. It is by Energy Saving Products in Alberta. The system is similar in principle and construction to a Unico system.

We use it for our home's cooling with a heat pump outdoor unit (we don't use the heat feature due to cost of electricity versus gas) and for humidification with a steam humidifier.

Today, the blower motor started vibrating violently. I removed it and found that the direct drive blower shaft has 3/16" end play and some up-down play. So, a new motor is in order.

But, while I have the system down for repair, a thought came to mind. I'd like to use a flexible connector between the unit's exit and the 8 inch round main duct. The hope is that the flex connector will remove some transmitted noise. What I'm trying to describe is similar to those seen on domestic forced air furnaces, just above the furnace where the metal duct attaches.

The cabinet is rectangular and at the end is a round take-off fitting (8") that has 8" 26 gauge round, steel duct attached. The round duct is the main "trunk" and has branches of smaller diameter metal, round duct; each of which eventually get 2" flex tubing for each room. Between the cabinet and the round duct is where I'd like noise isolation.

The unit lays horizontally on three strips of unistrut with vibrasorb pads between the strut and the unit's cabinet. The strut is hung from the rafters above. (I really, really wish I'd installed this vertically, like a hot air furnace, instead. Service would be so much easier. But, I had to get greedy about saving floor space.)

I could not find a round flexible connector for duct on line. The 2 local wholesalers said they don't exist in round.

What I am wondering is if a rubber pipe coupling, similar to a Fernco, would be OK to use. I'd cut a short piece (maybe 1/4") of round duct out and bridge the gap with the rubber coupling. Since we don't send hot air through the system, do you think that would be Kosher?

Or, can you think of a better plan to put some anti-vibration spacer in the duct?

Thanks Very Much for your thoughts and ideas about my plan!


  • Steve MinnichSteve Minnich Member Posts: 2,540
    I would find the source of vibration. When you pull the blower, check the wheel to see if it spins true. If its warped its going to cause all kinds of noise when it spins at full rpm. Any debris on the wheel is going to cause issues as well.
    PHC News Columnist
    Minnich Hydronic Consulting & Design, LLC
  • HVACNUTHVACNUT Member Posts: 3,348
    It's simply called a canvas.
    That's what they used to be made of.
    A local sheetmetal shop can make it. They come in two widths. 2" or 4".
    Just ask for a 8" round small or large canvas.
    Crimped on one side?

    Are there vibration pads at the A/H supports?
    Is it possible the motor, fan or mounting bracket is causing the vibration?

    If you replace the motor, replace the fan too. It's worth it.
  • Steve MinnichSteve Minnich Member Posts: 2,540
    I wouldn't recommend a canvas connector for a high velocity system.
    PHC News Columnist
    Minnich Hydronic Consulting & Design, LLC
  • STEVEusaPASTEVEusaPA Member Posts: 4,132
    If you're changing the motor, change the blower wheel too, and check the motor mounts for wear/replace if needed.
  • PGB1PGB1 Member Posts: 17
    Thanks Guys! for helping out. I sure appreciate the education.

    The wheel looks very clean & without debris. I wonder if the shaft play is what is causing the vibration.

    On the bench, it vibrates, too- so that eliminates random loose part in the air handler shaking in the wind.

    So there's either a warp, that Steve mentioned & that I can't see, or the shaft's bearings are worn.

    I got hijacked from the project today, so I haven't disassembled the wheel from the motor yet. Last time I was in there, I put anti-seize on the shaft, so it should come apart without damaging the housing. (It's an OEM only blower housing, so a quick total-unit swap is void on this machine. And it is crazy expensive. The motor, happily, is a standard 1/3 HP 3-Speed.

    Thanks HVAC Nut for the tip about a local sheetmetal shop. Crimping one side is genius. It'll be a super simple retrofit that way. There's a great family owned sheet metal shop which specializes in HVAC that I dealt with for years when working. They are about an hour away, but I like spending at family owned businesses when ever possible. Really nice people, too.

    About the vibration pad location- The manufacturer specifies that this unit can be horizontal, but doesn't have certain places for supports. The assembly is one main cabinet with a shorter cabinet for the evaporator attached to one end of the main cabinet. I placed one strut/pad under each end of the main cabinet (30" apart) and one under the end of the evaporator cabinet, 8" from the previous support.

    Thanks Steve USA PA for the word about changing the wheel. Since this is such a time consuming project to R&R the motor, I'll surely take your advice. Cheap insurance!
    The motor mounts still look good, but since I'm in there, I might as well start with a fresh set.

    Steve, you mentioned not using a canvas on high velocity. I'd imagine your advice is based on the high static pressure. (Guess I should have thought of that on my own...) Do you think the rubber pipe coupling would be OK?

    Thanks Again All!
  • Steve MinnichSteve Minnich Member Posts: 2,540
    @PGB1 - I don't think you're going to need it. When you pull the entire blower, just spin the wheel while its all still assembled. If its wobbly, it needs to go.
    PHC News Columnist
    Minnich Hydronic Consulting & Design, LLC
  • PGB1PGB1 Member Posts: 17
    Thanks Steve!
    After disassembling & bench testing, the motor bearing(s) is (are) worn. With no wheel on the motor, the motor rattles at low and medium speed. High is silent.
    Runout is not bad with the blower wheel off, but the rattling noise is a concern. I'll try it with the wheel on when I get a few minutes of peace later today or tomorrow.

    I am hoping that the wheel is OK.
    I have had no luck finding the size on line. It's 10-9/16" Diameter 4-1/2 total width 1/2" bore double inlet and is clockwise when viewing the hub end. (That's assuming I remember how to measure. Total width of the entire unit and total diameter.)

    After I get a motor, I'll re-assemble to test. If the wheel is bad, I'm against a problem finding one.

    Thankfully, we don't need this air handler for heating, so I've got some time to search. Humidity will be via pans of water on the radiators- like we used to do when we were younger.
  • Steve MinnichSteve Minnich Member Posts: 2,540
    Your best bet is to get Hi-Vs part list, get the OEM part for the wheel, and then do a search on the internet.
    PHC News Columnist
    Minnich Hydronic Consulting & Design, LLC
  • PGB1PGB1 Member Posts: 17
    Thanks Steve.
    Apparently the wheel is only sold with the housing (no motor). It is over $200.00. When I finally get a chance to buy a motor, I'll test with the old wheel and hope for the best. (Glad it isn't my heat, so I have some time to test things.)
    If it's no good, I'll bite the proverbial bullet and buy the housing/wheel combination.

    In the mean time, I'll keep searching for that size wheel alone. I'm having a hard time believing it's custom to the unit. Maybe I searched wrong.

    Thanks Again!
  • PGB1PGB1 Member Posts: 17
    Up & Running!
    Thankfully this unit is in my house & I have the luxury of time to repair it.

    I believe that the wheel being out-of-balance caused the motor bearings to wear, allowing too much shaft runout.

    In defense of the motor, it runs- mostly at a low speed- for 24 hours a day and has been going for about 11 years. (We have a PWM controller upstairs, installed like a lighting dimmer would be, and my wife can set the blower speed to her liking. Upon a call for cooling or humidity, the fan moves to the appropriate speed.)

    The "Non Standard" Repairs-
    First I bought a new motor. The windings were defective on it, so the vendor said to keep it, refunding the cost.
    I took the end bells (with bearings) off the new motor and put them on the old motor. Now I had a smoothly running motor: A Franken-Motor, but a working motor. (Free, at that)

    The wheel was now confirmed to be out-of-balance. By happenstance, one of my brothers stopped by and saw this on the bench. He inquired what I was doing. I mentioned that I was going to the local motor repair shop to pick up some balancing weights. He suggested tinnerman's nuts. The man is a genius!

    First I de-rusted the wheel and sprayed it with cold galvanizing compound. It took several days to dry in the cold garage. (As expected)

    For balancing, I ended up using one tinnerman nut from my stock, opposite the heavy spot. grinding away a small portion at a time to get the weight just right.

    The blower now is so smooth at all speeds, I don't think I'll have to put in any kind of flexible boot as a vibration eliminator. It will be interesting to see how long my "repairs" last.

    Thank You Again to everyone for helping me with this and for the education!

    Enjoy This Day!
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