Results 1 to 11 of 11
  1. #1
    Join Date
    Apr 2009
    Location
    British Columbia, Canada
    Posts
    38

    Furnace Retrofits - Plenum Questions (pops and bangs)

    Hey all,

    I have been doing commercial HVAC service for quite a while but just recently just started working with a company that mainly tackles residential HVAC. I have been doing installs of high efficiency furnaces lately (Lennox). The Canadian government had a lot of incentives for higher efficiency equipment and people have been racing to make the deadline.

    When installing plenums I have been taught to score the metal as it allows it to flex. Other then making sure everything fits nicely and using the appropriate S's and Drives what else can one do to eliminate pops and bangs? Is it normal to put canvas (vibration reducers) on all jobs? -return, supply, both? As well, the metal this company uses is 22 gauge - does this sound normal?

    I am a little bit of a perfectionist and if I ever pick up my own jobs I would like to make sure the finished product hits the Refrigeration/HVAC bar, or as close too!

    Any advice or knowledge would be appreciated.

  2. #2
    Join Date
    Mar 2013
    Location
    Joplin,Missouri
    Posts
    310
    22 guage is commercial grade metal is the plenum insulated? Are they properly sized? What kind of high efficency equipment are you using? Maybe SLP98 units for gas and CBX40 units for electric air handlers those are both variable speed units. If you have them installed with an icomfort stat you can slow down the heating and cooling cfm from the thermostat. You could make stiffeners and screw them to the plenum if all else fails but a i personally dont like the way it can looks you may have a sizing issue 22 guage metal properly crossbroke should not bang at all most placed just use 26 guuage for residential

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,104
    Are you actually getting popping and banging noises.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  4. #4
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,049
    I don't see 22ga metal popping and banging with resi size blowers. We use 26ga and rarely have duct bang issues, as long as its cross broken and sized big enough you shouldn't have an issue.

  5. #5
    Join Date
    Nov 2012
    Location
    Dublin, CA
    Posts
    121
    22GA is crazy for most residential applications. I make duct that are like, 36" x 36" in 22 GA. 24GA is pretty standard for a decent ductwork job on residential. 26GA is pretty thin, but doable.

    Vibration reduction, I've never seen that used in a typical residential application. Honestly, I can only think of one where it was used. The rest of the time I've used it was on commercial jobs.

  6. #6
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,588
    Try a double cross break, and also if you don't have enuf duct you may be getting those noises from high pressure? I will sometimes use a canvass connector just when the old plenum is against a ceiling and I don't want to fight for an hour. 26 ga is fine for resi, unless it's a mobile home then I think your supposed to use tin foil?

  7. #7
    Join Date
    Apr 2009
    Location
    British Columbia, Canada
    Posts
    38
    Quote Originally Posted by beenthere View Post
    Are you actually getting popping and banging noises.
    I also do the service side of things and had a 3 jobs with some pretty decent banging issues. Turns out they weren't scored and one had a jumper between W1 and W2. Customers haven't called back. Nor have I had any call backs on my installs...yet. (fingers crossed)

    As well, I realized the metal we use is 26 gauge. Not 22!

    Thanks for the replies. I have never really been a sheet metal guy into now. I like learning though.

  8. #8
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,588
    Some need the jumper so the second stage will kick on.

  9. #9
    Join Date
    Apr 2009
    Location
    British Columbia, Canada
    Posts
    38
    Quote Originally Posted by Joehvac25 View Post
    Some need the jumper so the second stage will kick on.
    What brand have you seen that on? I have only run into the timed controls. W1 stays energized for 7 mins, then moves to W2 if the thermostat is not satisfied..etc.

    Also, with many of these retrofits most customers do not want to pay more money for their ducting to be sized correctly. Running into noisy plenums has happened to me a couple of times now. The iComfort stats help as you can reduce the fan speed.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,104
    I find few, very few houses that need a furnace anywhere near the size he original one was. Often a 100,000 BTU in a house that only needs a 60,000. Usually the duct work is large enough for the 60,000. See a lot of companies that stick in a 80,000, and the duct work is too small for it.

    Might want to double check if the house really needs the size furnace your installing.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  11. #11
    Join Date
    Apr 2009
    Location
    British Columbia, Canada
    Posts
    38
    Quote Originally Posted by beenthere View Post
    I find few, very few houses that need a furnace anywhere near the size he original one was. Often a 100,000 BTU in a house that only needs a 60,000. Usually the duct work is large enough for the 60,000. See a lot of companies that stick in a 80,000, and the duct work is too small for it.

    Might want to double check if the house really needs the size furnace your installing.
    Agreed. I did the first couple of work orders without to much thought into how the salesperson sold. I am starting to see the differences between commercial and residential. I see a lot more installation issues and tons of little things are overlooked.

    Don't even get me started on those Lennox SLP's.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event