I have a really limited attic space - 22” from the top of the trusses to the the bottom of the 2 x 4s under the apex of the roof, then a low slope from there) with a bunch of angled supporting studs taking up space every two feet.
I need to fit a supply box that will have 10 ducts coming out of it, 5 off one side, 3 off the other and 2 off the back. I need to know how much space there needs to be between duct openings in the box. A salesman told me there needs to be 1” between them, and I want to see if he’s right, and also does the 1” refer to the space between the actual duct, or between where the insulation on each ends?
For example, if I have two 8” ducts side by side, and they are 10” with insulation, do I need to 17” total space (8 plus 8 plus 1), or do I need 21” total space (10 plus 10 plus 1)? The question still applies if 2 inches is needed – is it 2” between the actual ducts or 2” between where the insulation ends – do I need 18” total space or 22” total space?
Also does there need to be 1 inch between the edge of the box and a duct hole, or can an hole go right up to the edge?
Does it matter how big a box is relative to the size of the unit. I ask because it looks like my box would be about 20” x 22” x 64” for a 3.5 ton package unit due to the studs. It would likely be put about 22 feet from the wall where the supply trunk duct line enters the attic. The supply duct runs coming off it will be about 8 to 22 feet long. Does making the supply box smaller than the above have a benefit, and how large would the benefit be? I could potentially get it to be 20 x 19 x 60 depending on the answers to how far the holes need to be apart, and if they can come up to the edge, and where the studs are located. I'm not even sure I can fit a 20” x 22” x 64” box, which is why I need to know these things.