"Don Phillips" wrote in message
news:FUMXd.16875$i6.4990@edtnps90...

I have an upflow forced air furnace to which I added a 3-ton air
conditioner. The uncased A-coil sits in the plenum above the furnace. I
have a question regarding airflow. Approximately 5 ½ feet above the top
of the furnace is a square right angle to carry the air horizontally
across the bottom of the first floor joists. Approximately 4 feet from
that right angle is a second square right angle directing the air into
the main duct for distribution throughout the house. My question relates
to these right angles. Would it be beneficial to the airflow to change
the second square right angle to a curved one? Would a curve not improve
the flow? My concern stems from the fact I have 3 X 10 registers
throughout the house, since originally there was no air conditioning. I
have been told I should have 4 X 10 registers for the A/C. I know of no
way I can make the change, therefore I’m looking to find any way I can
to improve the airflow. If there is a way for me to change the
registers, I’m prepared to do that. The unfinished basement portion is
no problem, it’s the finished area of the house that is a concern. I’d
appreciate any suggestions you might offer. Thanks.


Every 90 is the same as 10 feet of straight duct. Turning vanes MIGHT help
some.
Eventually the duct pressurizes and the air travels where the pressure is
lowest.