This is a camp and it's post and beam so there are no studs in the walls. From the drawings, it appears it goes from 1" monasote panels to 2" foam to 1" siding which doesn't leave me anything to really attach this unit to in the wall. My initial thought was to use through bolts all the way to the outside to hold it against the siding, would this be strong enough? Any other ideas?

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  • 1
    The drawing says Homasote, not "Monosote" (if the latter is even a thing.) Homasote® is a thing, but not one I'd try to hang a compressor unit off of, as it's essentially thick paper, and will crush if loaded by bolts.
    – Ecnerwal
    Commented Jul 27, 2023 at 18:53

2 Answers 2


Question did not specify, so I answered for the external unit: Use suitable legs to support it from the ground near the house. They are standard, they work (get tall enough for the snow in the area) and they don't depend on dodgy anchoring schemes, or trying to get long screws into the framing (while missing wiring that may be invisibly channeled in the back of the framing.)

Since it's been clarified that it's the internal unit: Attach to the post and beam framing directly, or via sub-framing attached to the post and beam frame.

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    This is for the indoor component, I'm not understanding how legs would work for this Commented Jul 27, 2023 at 19:23

Definitely recommend against drilling all the way throught the walls.


  1. Add exposed framing that the air handler can be attached to with wood screws. Could use the same or similar wood type as the posts and beams and stain or paint to match the existing framing. Or could just use KD 2x lumber.

  2. Rig metal supports.

EDIT I no longer propose 3. For one thing it would put holes in the insulation layer. It would be much better to attach new framing to the existing exposed framing and attach the air handler to that.

  1. Attach directly to the masonite using appropriate anchors. Masonite backed by styrofoam will support a mini-split air handler.


Even though the backing plate for the air handler is secured by a limited number of screws it may be best for it supported over its full area. A piece of plywood (1/2", 5/8", 3/4"?) fastened to two vertical framing members should serve.

The only question would be should the plywood be positioned right next to the Homasote or should there be a gap of several inches between the back of the plywood and the Homasote.


Since this is a post and beam construction a pair of extra vertical 2x4s might detract from the interior visual effect of the posts and beams. To detract less a pair of angle steel vertical elements could be bridged by a piece of plywood that the backing of the air handler would be screwed to. The angle steel could be painted either black or architectural bronze. The plywood (which would be hardly visible) could be painted black or stained to match the interior posts and beams.

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    Regarding 3, what type of anchors would be required that would hold in styrofoam? The monasote is like paper but maybe a spread anchor that goes through and spreads out on the backside might hold Something like m.media-amazon.com/images/I/71aMLb6DLtL._SL1500_.jpg Commented Jul 27, 2023 at 16:07
  • Do not know know what monasote is. I thought this must be like masonite. Much prefer options 1 or 2. Anchors might not open up in styrofoam. My option 3 is highly questionable. Recommend you ask builders of this type of structure how they install minisplit air handlers in new construction. Commented Jul 27, 2023 at 16:11
  • Exactly where do you want to mount the air handler? Commented Jul 27, 2023 at 21:12

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