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Supporting frame for new HVAC unit

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  1. #1
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    Default Supporting frame for new HVAC unit

    Hello

    I need to build a drop ceiling for a new HVAC unit that I need to install. The HVAC unit weighs 82kg and is 500 (H) x 1430 (W) x 970 (D).

    Per the diagram below, there will be a timber support underneath the HVAC unit, which will be supported on a stud on one side and hung from the floor joists on the other side. The stud will be <3m high on one side and the hanging support <500mm high on the other side.

    I have looked at the span tables for MGP10 in AS1684. Can tables 6 and 7 be applied in this situation? Understand these aren't floor joists, but the arrangement is similar to what a floor joist would be doing. Plus the loading provided as a basis for these tables far outweighs my 82kg HVAC unit.

    If I assume 300mm spacing between timber used to support the HVAC unit, table 6 yields a 120x35 timber support which will get me a 2400 span (I need 2200).

    For the side supported on stud, table 7 states that a single 90x35 stud will do the job with a RLW up to 7.5m (I only have 2200).

    For the side hung from the joists, I was planning to use 90x35 timbers, fixing them to the side of the joists and then to each 120x35 timber member.

    Was planning to use 10g screws to secure everything together, each screw being good for about 40kg (obviously using multiple screws at each support).

    Appreciate any advice anyone has for me.
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  2. #2
    Seasoned DIY droog's Avatar
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    Assuming this is under the floor and is not hanging above a habitable room then what is stopping building a platform with support to the ground ?
    This will also help with isolating the unit for noise reduction.

    If it has to be hung then keep in mind an average person would be about the same weight, so just an extra person standing in that part of the room.

  3. #3
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    Quote Originally Posted by droog View Post
    Assuming this is under the floor and is not hanging above a habitable room then what is stopping building a platform with support to the ground ?
    This will also help with isolating the unit for noise reduction.

    If it has to be hung then keep in mind an average person would be about the same weight, so just an extra person standing in that part of the room.
    Thanks for the response. This is a double storey house. The structure is going to be built in a rumpus room which has another floor above it. If I add another support on the other side to ground, it will impede the room.

  4. #4
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    FWIW although I love working in timber I believe steel could be a better bet here. Smaller sections will be required for the same span.
    And.....your point is.....what exactly?

  5. #5
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    Quote Originally Posted by David.Elliott View Post
    FWIW although I love working in timber I believe steel could be a better bet here. Smaller sections will be required for the same span.
    Thanks for the response. Steel is going to be hard work for me as I have no idea how to weld.

    I have actually gone one step further and done some bending and deflection calculations and I can get away with 90x45 MGP10 members with joist hangers instead of using the span tables in AS which are an overkill for this scenario

  6. #6
    4K Club Member Marc's Avatar
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    Buy galvanised RHS and mount it by drilling and trough bolting or U bolts. No need for welding, in fact I wouldn't recommend welding at all unless you are a good fabricator
    Enjoy present pleasures in such a way as not to injure future ones.
    Seneca

  7. #7
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    Are you rigidly attaching the platform to the walls and floor? I'm wondering because down the line I have to build my own HVAC platform and I was intending to find some failsafe rubber mounts to hang the platform. Haven't looked lately but there's specific products for this application. The floor is a giant diaphragm, causing the vibrations from the unit to propagate through the house. Same problem if the platform is in contact with a ceiling. I assume modern units do a pretty good job of reducing vibration in the first place, but it's a hard problem to fix after you've built the platform.

  8. #8
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    Quote Originally Posted by Jonno80 View Post
    Are you rigidly attaching the platform to the walls and floor? I'm wondering because down the line I have to build my own HVAC platform and I was intending to find some failsafe rubber mounts to hang the platform. Haven't looked lately but there's specific products for this application. The floor is a giant diaphragm, causing the vibrations from the unit to propagate through the house. Same problem if the platform is in contact with a ceiling. I assume modern units do a pretty good job of reducing vibration in the first place, but it's a hard problem to fix after you've built the platform.
    Well this was the plan until I got my hands on the installation manual for the air handling unit. It has brackets either side so you can hang this thing up with threaded rod from the joists themselves.

    So this design pretty much goes out the window now lol.

  9. #9
    Golden Member manofaus's Avatar
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    but were the joists designed to have a dead load?
    sorry for the ramble.

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