Ducts at end of Supply Plenum?
 

I am having some work done on my existing HVAC system have met with 2
contractors.

One contractor has pointed out that I have several ducts at the end of my
supply plenum and that is a NO-NO. He suggest that this should be corrected
by making the supply plenum larger and having all ducts come off of the
sides of the plenum. Another contractor is not concerned about this and
suggest that the use of manual dampers is sufficient.

How much of a NO-NO is it to put supply ducts at the end of the supply
plenum? We could use better air flow at the ends of the house and I was
wondering if the larger plenum with all ducts to the side would help.

Thanks for any advice you can provide.

George

How much of a NO-NO is it to put supply ducts at the end of the supply
plenum? We could use better air flow at the ends of the house and I was
wondering if the larger plenum with all ducts to the side would help.

Simple laws of physics always work. You want more air flow, use larger ducts.
Too many HVAC installers make tidy looking installations that disregard simple
rules. Maximum airflow depends on plenum and blower design and should follow
manufacturer's recommendations.
Your post will likely trigger many responses from HVAC experts. Some may have
practical advice for your situation. You may even need to talk to one or more
other contractors to arrive at a logical conclusion. Good luck.
Joe

George Sambataro wrote:
I am having some work done on my existing HVAC system have met with 2
contractors.

One contractor has pointed out that I have several ducts at the end of my
supply plenum and that is a NO-NO. He suggest that this should be
corrected
by making the supply plenum larger and having all ducts come off of the
sides of the plenum. Another contractor is not concerned about this and
suggest that the use of manual dampers is sufficient.

How much of a NO-NO is it to put supply ducts at the end of the supply
plenum? We could use better air flow at the ends of the house and I was
wondering if the larger plenum with all ducts to the side would help.

Thanks for any advice you can provide.

George

To answer your last question, someone there will need to do the work of
measuring what you have and doing the numbers to determine what you need
using, I believe, that Manual J calculations or is it "D" I don't do this
work so I don't really remember.


--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

George;

Yes, it is considered 'not a good idea' to take branch runs from the end of
the plenum unless it is an 'extended plenum of considerable length.'
Residential duct systems run at a very low static pressure and if the branch
takeoffs are directly facing the blower, there's a tendency for the pressure
to take the path of the least resistance. It's better if the branches take
from the sides so all the ducts are pressured the same. (Although sometimes
that's just not possible.)

Dampers are fine for 'small balancing' but not recommended for large
corrections. Dampers will not 'increase the pressure' in adjacent ducts,
but will reduce the air flow. It's dependent on the design of the ducts (if
it was designed at all.) ACCA Manual J is for load calculations on a
Residential / Light Commercial Building and ACCA Manual D is for designing
low pressure duct systems. You should seek a licensed HVACR contractor who
uses these guides for design work on your HVAC.

The best way to find a reputable contractor for you would be to seek
recommendations from your friends, relatives and neighbors. If they had any
'bad experiences' they'd let ya know. And please don't get more than 3 - 5
quotes. It does cost for a contractor to give a bid.

What exactly is it you want to do? Or what problem are you solving?

--
Zyp

"George Sambataro" wrote in message
...
I am having some work done on my existing HVAC system have met with 2
contractors.

One contractor has pointed out that I have several ducts at the end of my
supply plenum and that is a NO-NO. He suggest that this should be
corrected
by making the supply plenum larger and having all ducts come off of the
sides of the plenum. Another contractor is not concerned about this and
suggest that the use of manual dampers is sufficient.

How much of a NO-NO is it to put supply ducts at the end of the supply
plenum? We could use better air flow at the ends of the house and I was
wondering if the larger plenum with all ducts to the side would help.

Thanks for any advice you can provide.

George

"George Sambataro" wrote:

How much of a NO-NO is it to put supply ducts at the end of the supply
plenum? We could use better air flow at the ends of the house and I was
wondering if the larger plenum with all ducts to the side would help.

Yes and no. You need a larger duct feeding the it to flow more air, and
it needs to be reduced in size as it goes along, to keep the pressure
(?) up.

I remember seeing a laboratory in a national lab, built after WWII to
hold a room full of vacuum tube counting equipment. Talk about a cooling
load!

The ducts were like 2'x4' at the beginning and ran to the end of the
room, and had ducts coming out every foot on both sides, and shrunk by
like one inch after each pair of ducts, until it was just a single 8"
for the last pair. I was there in the 70's and what had been a 6' rack
cabinet had shrunk down to about an inch wide in a rack chassis.

Even in modern houses, I see that, where the main air duct reduces down
in size, after feeding ductwork.

....and this reply helps the OP, how?

"Joe Bobst" wrote in message
...
How much of a NO-NO is it to put supply ducts at the end of the supply
plenum? We could use better air flow at the ends of the house and I was
wondering if the larger plenum with all ducts to the side would help.

Simple laws of physics always work. You want more air flow, use larger
ducts.
Too many HVAC installers make tidy looking installations that disregard
simple
rules. Maximum airflow depends on plenum and blower design and should
follow
manufacturer's recommendations.
Your post will likely trigger many responses from HVAC experts. Some may
have
practical advice for your situation. You may even need to talk to one or
more
other contractors to arrive at a logical conclusion. Good luck.
Joe