All round ductwork?

[enigma]

Installer says that all round ductwork has a better airflow than the existing square one and he will install all round ductwork - is this right?

[airconman]

depends on what size you have.... usually to get best air flow you have a square trunk line with round pipe coming off it....
a six inch round pipe is around 100 cfm 105
a seven inch is around 150
8 230
square is 12x8 around 500
14 x 8 is 600 etc etc etc...
your furnace has a 3 ton blower or 4 or what ever
1 ton equals 400 cfm..... so 3 ton is 1200 etc.
make sure you have enough air innnnnn and enough air outttttt so you don't have heat exchanger problems early in system....

[heatpumpman]

If all the design parameters are correct.

[johnl45]

[johnl45]

One common practice is rectangular trunks with round run-outs. Proper sizing is more important than round or square.

[corny]

a properly sized round duct system will deliver the air more efficiently than a square or rectangular system....even with rectangular duct...the closer you get the two dimensions closer to a square shape the better the airflow through the duct. round is best because the air moving thru it exerts an equal pressure along the interior of the ducting and this results in smoother more efficient airflow.

The biggest reason people are going to round now is that it is easier to install and cheaper as it actually takes less metal than square or rectangular equivalents. But its better for you the consumer because you are pretty well assured of getting a better sealed system with round pipe...Ive seen countless rectangular duct systems with leaks you could stick your hand thru where the installer couldnt get the duct connected properly and just gave up and taped over the gaping hole left where the connector goes.....tape eventually works loose and you have a massive air leak.

I once tore out a whole system where the installers just jammed the rectangular duct together without using the S lock and drive cleat connectors...it was jammed together and the joints taped....when the system would come on the insulation around the duct would balloon out...the original installers were not fly by nights either...they had been doing business for some time and still are today.

[Steve Wiggins]

Good post corny .......but what about noise issues?

[bluetooth751]

Originally posted by heatpumpman
If all the design parameters are correct.

Square or round?

ROUND YES

Exactly

[dash]

A round duct system is no more efficient than a square one ,with comparable design,same goes for flex duct.

Round will consume less sheet metal to get the same airflow,but that doesn't mean it will be more efficient.Same goes for sq. versus rectangular,rectangular wil consume more metal for the same airflow.

There is one small advantage,since it takes less sheet metal to handle the same airflow,it takes less insulation,so the end result will have slightly less duct loss,due to temperature difference.

[dec]

[QUOTE]Originally posted by dash
[B]A round duct system is no more efficient than a square one ,with comparable design,same goes for flex duct.

QUOTE]

Well I may be wrong but I was always under the impression that round if sized right and of same material (flex would be differant) would have better air flow characteristics then square or rectangle. That being that with the square corners ,that would cause more friction , turblence and tumbling of the airflow as compared to round. I may be wrong but it always made sense to me . In my opinion more square is better then retangular but round is better then square.

[enigma]

I've been told I'm a good tester (testing person). Whatever I stumble on or use I find unusual problems, bugs or questions. So there comes another one for this forum:

How about a TRIANGULAR duct vs. SQUARE duct?
Also: OVAL vs. ROUND.

:-)

[dash]

12" round,10"X11",and 21"X6",all have the same airflow characteristics ,except velociy which will be less in the 10X11 and even less in the 21X6,assuming the same material.Check your ductolator,to verify.

[dec]

hummmm .... I have no idea how to go about making triangular offsets and elbows. I think I will stay away from the triangular conversation in that case. Altho I have seen a little triangular duct run down trusses but when it came to the connections where it adapted to the round or rectangular duct ,it wasnt any connection that would create good air flow.

[Edited by dec on 01-29-2005 at 02:45 PM]

[dec]

Originally posted by dash
12" round,10"X11",and 21"X6",all have the same airflow characteristics ,except velociy which will be less in the 10X11 and even less in the 21X6,assuming the same material.Check your ductolator,to verify.

Well everytime I get a customer that wants to save ceiling height by making the ductwork 2 inches deep by 40 inches wide I tell him it just wont let the air flow right being its all surface area and the air wont flow right.



THATS MY STORY AND IM STICKING TO IT......

[johnl45]

Originally posted by dec

Originally posted by dash
12" round,10"X11",and 21"X6",all have the same airflow characteristics ,except velociy which will be less in the 10X11 and even less in the 21X6,assuming the same material.Check your ductolator,to verify.

Well everytime I get a customer that wants to save ceiling height by making the ductwork 2 inches deep by 40 inches wide I tell him it just wont let the air flow right being its all surface area and the air wont flow right.



THATS MY STORY AND IM STICKING TO IT......

Quote the cost of 2 X 40 and he'll change his mind real quick!

[corny]

For noise issues you should just size your duct correctly for the proper fpm as well as cfm.....