Does anyone know if it is OK to install a new duct collar to the back wall of the HVAC "supply box"/plenum? That is, on the end of it, where the squirrel cage blower is blowing directly towards.

Or, can you only have ducts leaving the sides of it so all the blowing air hits that back wall and reflects backwards to pressurize the box?

Thanks in advance.

As my handle indicates, this is well outside of my realm. However, having dealt with issues in the past while remodeling, i have run into this. It is my understanding that this is not an acceptable means of adding a duct. In fact, even when coming off perpendicularly, the duct is supposed to be a certain distance from the end of the plenum. It is my understanding that you will end up with a crap ton of air and pressure that direction and everything else will suffer. Again, take my commentary with a grain of salt, but that is my understanding that it's not OK.

I believe there is an 18" requirement from the back of the wall and the idea is that pressure should build from there to the front to each of your branch ducts. I think....

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I believe there is an 18" requirement from the back of the wall and the idea is that pressure should build from there to the front to each of your branch ducts. I think....

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Thanks, and that would make complete sense. I think I am just going to see if I have a slot I can cutout further away from that back wall so I keep a good pressure buildup in there.

To piggyback, your longest branch runs should be closer to the end of the plenum, while the shorter runs should be closer to the blower.

Ditto what Jason said....do NOT put in on the end of the plenum opposite the blower....never.....never.....never!!

Thanks all for the replies. I really appreciate the help.