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.

On Tuesday, June 9, 2020 at 9:58:20 PM UTC-4, Davej wrote:
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.

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.

On Wednesday, June 10, 2020 at 7:15:05 AM UTC-5, trader_4 wrote:
On Tuesday, June 9, 2020 at 9:58:20 PM UTC-4, Davej wrote:
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.

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.

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.

On Wednesday, June 10, 2020 at 8:57:37 AM UTC-4, Davej wrote:
On Wednesday, June 10, 2020 at 7:15:05 AM UTC-5, trader_4 wrote:
On Tuesday, June 9, 2020 at 9:58:20 PM UTC-4, Davej wrote:
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.

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.

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.

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.