Re-routing upstairs HVAC airflow?

[Davej]

Once again I am frustrated by the typical upstairs HVAC airflow scheme. The return air goes into a vent on the wall and flows upward to a plenum in the unconditioned attic crawlspace. The plenum then travels about eight feet and then comes down to the HVAC unit where it enters the filter just above floor level. The output of the HVAC then goes up to another much longer plenum in the unconditioned crawlspace where a pipe for each vent is connected.

I don't believe this scheme is efficient or effective so tomorrow I'm going to disconnect both plenums from the HVAC and experiment with some simplified airflow schemes. I think the return air has absolutely no need to go up and through the unconditioned crawlspace -- that setup is just silly. The output air will be a more difficult and complicated problem, but mostly I want good airflow to the upstairs den so I will route the air there and see how well that works.

[trader_4]

Where is the HVAC? In the attic or upper living space floor? Here they put them in the attic, which makes routing simpler and better, but the whole idea of running any of that in the attic must result in a lot of energy wasted. If the HVAC is on the upper living space floor, I would agree that pulling the return air locally instead of from a return going through the attic is worth a try. The problem though would be rooms that have doors, when they are closed there will be no return airflow.

Might be time for new construction ideas, like adding a foot between upper floor and attic for ducts to run where they can be well enclosed, insulated, etc. But that would add $$ to construction cost, so not likely. One solution to problem systems like this would be adding minisplit AC.

[Davej]

Yes, the HVAC is in a centrally located upstairs closet. The upstairs floor plan consists of a den and four tiny bedrooms. Only the den and one of the bedrooms have return vents to provide the air to the return plenum, so that whole thing seems fairly pointless. Overall the airflow seems bad.

[trader_4]

You probably already know this, but you shouldn't just pull the return air from the closet, even with a vent in the door, if there is a furnace involved.