HVAC ducting question

[porsche4life]

Wondering if one of you guys can help me understand why my Return registers are ducted the way they are. I’m working in a remodel project that requires me to move one of the registers and as I’m doing that I’ve realized that the way they are currently hooked up seems ass backwards. Their current placement means that one of the returns is placed on the opposite end of the unit from where it needs to be and is ducted around the unit, while the return for the second unit is placed where I would think the one for unit 1 needs to be and is ducted around unit 1 and through the attic.

Is there a reason that on a 4 ton unit with a 16” intake duct it would need to be routed 10-15’ instead of getting a short 2-4’ long duct and straight into the unit?

I’ll try to get a drawing for you guys to explain.

[porsche4life]

Crude drawing here. Current layout in my attic is as in red in green. The red return stays, and I’m adding the one shown in blue, thinking I will duct them as shown in blue when all done. Is there any reason that wouldn’t work?

[T77911S]

I don't know if this will help, not an expert by any means but I do do ( I said dodo) some HVAC work.

the return needs to be in the same "zone" or part of the house that the supply feeds for that unit.
the return should also be placed to cause air flow through the house to help circulate the air.


it sounds like you have a single story with 2 units?

[BK911]

Sorry, can't follow the drawing.
But besides airflow, noise is also a consideration.
Very little return ductwork with a straight path into a space will transmit fan noise into that space.
Need some duct mass and an elbow or two to reduce the noise.

[DerkPerk]

Both valid points here.

I agree that noise is a big factor. Having that addition length will not affect performance and can only reduce noise.

Also, creating airflow through the room is important to not short cycle the hot/cold air right back to your return. Your AC system will operate at a near 20* delta T so sending back return temps below 68* can sometimes be problematic.


Sent from my iPhone using Tapatalk

[porsche4life]

Good callout on the noise.

Yes 2 story house, both intakes are at the top landing area for the stairs so plenty of good airflow up, house also has passive ducting from downstairs to up to allow good circulation.

Thinking about the noise, I’ll just leave them ducted as is and relocate the intake for the one unit based on the need for my remodel.

[T77911S]

again, I don't do residential for a living.

"usually" the up and down are completely separate.
one return up, one down.
if you can convert it to that way you may consider it. '

its your house and you know the layout.
just keep in mind you want the air to flow BACK to the unit that is running.
I would "hope" the guys that put the system in did it the most efficient way, they usually don't want to waste money running unnecessary duct

[Tidybuoy]

I'm going to be relocating my A/C / Heater to the attic. Primary reason is to free up space in my house but another reason is noise. One of my current returns is 2 ft from the HVAC blower and it is noisier than hell.

[MBAtarga]

I've had good experiences in reducing the noise caused by high volume air flow in return vents by opening the vent slots further by prying with pliers to improve flow/volume.