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View Full Version : 8' -10' Duct lengths


Southern1
10-28-2009, 05:19 AM
Has anyone ever used 8' or 10' single joints of duct? It seems like it would be a little more work in the shop, but would cut field assembly time.

Just curious.

ccrayjr
10-28-2009, 09:07 AM
A lot of residential contractors use 8' duct. They take it to the job snap two L sections together and cut it to the size they need. It is a little more awkward to handle, but most cut it on their plasma table so it cuts shop time! With more and more redisential contractors buying coil lines, they are using more 5' now also!

Bounder
10-28-2009, 03:18 PM
8 or 10 foot joints are fine but SMACNA requires a heaver gauge or reinforcement the longer the duct. In housing I suppose you can do as you wish but my jobs were commercial with lots of requirements.

Did a study on it and found that once we went over 5' the gauge and reinforcements needed made the duct too expensive for anything over 10" wide.

greenman9
11-14-2009, 02:14 PM
I used to be asked to make 8' lengths of continuous duct, I hated it. I dident want to sound fussy but I had several reasons, It required 2 people at the brake usually pulling someone away from the shear, notcher or some other post. there was more likelyhood of a twist developing in the duct(especially if it was smaller) and it is awkward to line. In staging the duct it took up more floor space. the only 2 reasons I would consider having 8 or ten foot lengths is if the duct had to span a wall or if it is exposed and the termination was at a point beyond 4 foot.

However this is a shop guys point of view. I had a ten foot brake that was old and in need of maintenance, and I was usually short staffed. I think every shop would like more floor space, especially with more than one job going on and staging the work into areas for each job makes floor space even more valuable.

Rob
11-14-2009, 04:28 PM
Good reply greenman.
I worked alone for almost 30 years.
I always avoided using 8' duct for that reason.
For years around here production-run duct was sold in 4' lengths, now the suppliers have all changed to 5' lengths.
It's surprising how much of a difference that extra foot makes.
In fact, I'm so conditioned to using 4' duct, the other day I needed a piece of duct 39" long.
So, I cut 9" off of a pair of pr pieces, put them together, etc.
Went to put it up, and it was a foot too long. :oops:

greenman9
11-17-2009, 04:08 PM
Another good reason for going beyon 50" in length is that the duct will not fit in the beader. Speaking of beaders I have seen SM with beads run the length of the duct rather than across. It seems like that would be worthless to me. any thoughts?

cactassdupree
11-17-2009, 04:29 PM
I've use 10' on small stuff. U can always crossbreak it to give it a stiffy

cactassdupree
11-17-2009, 04:36 PM
Sorry I hit the wrong key and posted before i wanted to. I thought it would be a good idea to make some 6"X4" exhaust duct to get rid of a connection in the field. Well I was flipping it end for end turning the drive and didn't notice an open electrical box in the roof with bare wires (220V). I was wearing good rubber on my feet so I didn't feel anything. But, the thing sounded like a bolt of lighting went through the shop. The next day they fixed the elec box.

greenman9
11-17-2009, 05:13 PM
I was making some larger duct for duct-mate frames so the ends were raw, it was 18 or 20 ga. galv. one of my coworkers was assembling the frames and rolled the duct upright, when it hit the floor an extension cord was underneath and the duct acted like a guillotine blowing the circuit breaker.