Flexible Duct (How much is too much??)

[judgetc]

I have recently inquired about getting new adequate ductwork when i have my new furnace/ac unit installed. I was told by the installer that all the duct will be the flexible type. I've put the project on hold until i hear from youall on the mtn top. Does this sound right???I thought it could only be used in certain instances and lengths. What do the experts think????

[Gunnery Sergeant Hartman]

It'll be fine as long as its designed by Manual D.

[dash]

Flex will be fine,IF ,sized and installed properly,which is often ,Not the case.

Ask if they are using ManJ and Man. D??


Why are they suggesting replacing all the duct??What is not adequate??

[duc dowg]

nothing wrong with flex if straped up and seald good
does need to be sized right man d or j

[md master]

Depends on the application as well. Is it in a crawl space? if so the mice (all homes get em) will eat holes in them and make nests. This will obviously cause a serious leakage as well.

[ct2]

The company I work for does nothing but residential installations and thats all they use

[coolestacman]

I think the least amount of flex is best, origanly you use to see it to make the connection from the run to the difuser and a max of three feet. As with everything that comes alon to make ones life easier someone has to abuse it.

If the contractor wants to use flex send him away and get someone that can fab up duct. This would mean getting a reputable shop.

coolestacman

[md master]

Originally posted by coolestacman


If the contractor wants to use flex send him away and get someone that can fab up duct. This would mean getting a reputable shop.

coolestacman

Be prepared for higher prices, quality ain't cheap.

[tinknocker service tech]

true tinknockers are becoming a thing of the past in the resadential market. flex is fine as long as it is in your attic. if you main trunk is under the house in a crawl or basement should be all medal. and insulatated in all crawl spaces.

[rimek]

"Depends on the application as well. Is it in a crawl space? if so the mice (all homes get em) will eat holes in them and make nests. This will obviously cause a serious leakage as well."
__________________

See if you can get clear flex for the "habitrail" effect, then.

[tinner73]

all flex would never pass code by me. you're an ironworker......put some iron in. keep the flex down to a minimum.

[beenthere]

We prefer to run duct board trunk, then flex to the grilles, but if sized right nothing wrong with flex trunk.

Of course, sheet metal sized wrong is no better then flex sized wrong.

[Irascible]

Originally posted by coolestacman
If the contractor wants to use flex send him away and get someone that can fab up duct. This would mean getting a reputable shop.

Uh huh.

You might consider sending all union shops away too judgetc. A reputable shop has quality employees who are hired and paid on merit - not protected by irrelevant measures such as length of time served, how loud they can yell the word “scab” or what union boss they've sucked up to.

Yeah. I know. Such an analysis is absurd. But it's no more absurd than assuming that sheet metal is the only viable duct solution and that any shop using flex is therefore not reputable.

[bbk]

I installed real duct in the house I built for myself.
Flex has it's place...just not in my place.

[bornriding]

I never use flex duct as my trunk line.
Will run flex to branch outlets, no problem
If my flex run would be longer than 15 ft, would probably run some 'oversized' hard pipe and then reduce down to flex close to boot.
Flex only used in attic also.
All hard pipe, under house.
And I personally don't like ductboard so I don't use it.

[hvacbear]

As already stated flex was originally designed for connection from a metal trunk to a diffuser a few feet away. It does create more of a pressure loss than metal duct so that must be taken into account when sizing. I too am of the less flex the better persuasion.

[jeffkillen]

I'm an old tin knocker myself but I realize flex has it's place and is here to stay so what is one to say?

[tinner73]

i like flex........just in small doses.

[amickracing]

I like flex too... Cut a piece a few feet long, loop it so one end is pushed inside the other (so it makes a tight circle with no hole in the middle), paint it orange and ya got a pumkin!

I think flex has it's place, but the only place I actually like to use it is on the comercial jobs to hook up the diffusers to the duct, or in some cases in residental where hard piping from the duct to the register would be impossible with out a lot of elbows.

Personally if I have the choice, I never put flex where it can't be reached once the house is done (between floors or other similar places). In attics, I might use a few feet, crawlspaces only if there's absolutely no other way. Our code says 7' max, I try to stick to 3' myself.

[dan sw fl]

Originally posted by judgetc
I was told by the installer that all the duct will be the flexible type. What do the experts think????

Review the Manual D and J design.
If it does not exist, go onto the next shop.

Suggest to use adequately sized ( ~1,000 FPM) duct header of ~ 2 feet per ton at fan outlet.
i.e. 5-ton, 14"x20" about 10 feet long.

Flex limit of 20 feet on branch runs is good rule-of-thumb'.

Add Simple E.S.P. TEST as part of your contract:
Max. 0.2" in header, withhold 25% of total estimate until static pressure can be maintained at < 0.2". 0.3" if using a variable speed air handler.


[Edited by dan sw fl on 03-16-2005 at 06:54 AM]