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I had two furnaces installed in the attic last month. These are vertical units that they installed on the floor of the attic with the evaporator coil being on top of the furnace. I have attached some pics. I have a couple of concerns and wanted to get your input on these.
        
The weight of the furnaces is not supported by any ceiling joists, it's essentially sitting between the two ceiling joists on the plywood floor board. You can even see the floor board sagging a bit under it.  There is no other support for the unit.  Is this acceptable?  And if not what should I ask the contractor to do to fix it?
        
The cold air return round flex duct is connected directly to the furnace.  I think it's not good to have round flex ducts directly connected to the warm air supply, but what about on the cold air return?

unit 1a.jpg

unit 1b.jpg

unit 1c.jpg

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I had two furnaces installed in the attic last month. These are vertical units that they installed on the floor of the attic with the evaporator coil being on top of the furnace. I have attached some pics. I have a couple of concerns and wanted to get your input on these.
The weight of the furnaces is not supported by any ceiling joists, it's essentially sitting between the two ceiling joists on the plywood floor board. You can even see the floor board sagging a bit under it.  There is no other support for the unit.  Is this acceptable?  And if not what should I ask the contractor to do to fix it?

The weight of the furnace is distributed to the two ceiling joist via the plywood base.  The flexing of the plywood is proof that it's inadequate to the task.  The kicker is that I'm not aware of any code cite that covers that.  Show the photo to your tech and ask him to correct it.

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The cold air return round flex duct is connected directly to the furnace.  I think it's not good to have round flex ducts directly connected to the warm air supply, but what about on the cold air return?

I've always seen a 'square to round' adapter plenum installed between the indoor section and the flex main AR duct.  Punching a hole in the side of the indoor section housing to accommodate a duct is not something a manufacturer would support.  Also, at least 50% of the flex return air ducts I've seen (single AR duct designs only), were too small to carry the entire system volume.  An older cardboard duct size calculator I have says single AR ducts should have at least one square foot in cross sectional area for each ton of cooling installed and no more than about 5 foot long.  My 30 years experience in resid/light commercial supports that for most AC brands.  Consequence is freeze up under worst case conditions.

It's a really lousy idea to install vertical indoor sections in the attic unless it's a 1st story attic and the supply air is for upstairs rooms.  I'd love to write up that AC guy and see how red his face gets.

Edited by Marc
Added ranty comment
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Because I've never seen any AC indoor section come from the manufacturer with a large round hole in it for a flex duct.

I wouldn't bother with fixing that.  I mention it because it goes to the credibility and workmanship of the guy who did it.

A horizontal unit would've been my choice, laid across at least 2 bottom chords.

It can be remedied.  That model you have just might have a horiz option.  Just rotate the coil/primary drain pan 90 degrees.  If it doesn't have that option, get a different model.  The big question is who's going to pay for it.

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