Comments on: Don’t Kill Your Air Flow with This Flex Duct Disease

By: Frank

Frank — Sat, 22 Feb 2014 03:16:09 +0000

Flex duct needs to be
Flex duct needs to be installed closer then 5 feet and with something that is wider then 1 1/2"

By: David Butler

David Butler — Tue, 26 Feb 2013 09:20:08 +0000

@Chuck, I'm not sure flex has
@Chuck, I'm not sure flex has anything to do with the smell. Maybe a mouse crawled into your ducts and died?

I would have the evaporator coil and surrounds checked for mold. If that's the case, it may be related to blower or thermostat settings.

By: Chuck

Chuck — Tue, 26 Feb 2013 08:59:01 +0000

Had a new 16 seer Trane
Had a new 16 seer Trane straight cool air-conditioning unit put in a year ago. Their brand-new design. Had dirty 30 year old duckboards removed and new flex duct installed at same time. About two months later I noticed a smell I've been fighting ever since. Live in Florida. Smell is only present when AC is running, Not so bad when in heat mode. Can't figure this one out. Drain line is clear to outside.

By: Dale

Dale — Fri, 16 Nov 2012 21:29:46 +0000

Here is a GreeSpec listed
Here is a GreeSpec listed product (FlexRight) that solves many of the issues with flex duct installations. Product was invented by a HVAC contractor. http://www.flexright.net/residential.htm

By: David Butler

David Butler — Tue, 30 Oct 2012 00:49:39 +0000

No problem, Allison. It's all
No problem, Allison. It's all good. The fact that you thought I had changed positions meant that I didn't express my positions as clearly as I could have.

By: Allison Bailes

Allison Bailes — Tue, 30 Oct 2012 00:00:55 +0000

David B.:
David B.: I thought you were saying that you think flex should be outlawed when you said you "totally agree with JP regarding flex," so I guess our misunderstanding was on the interpretation of John's comment. I didn't intend to ascribe different meaning to your words and don't think that the part of your comment that I quoted was horribly out of context. The other sentences add some detail, but I think the sentence I quoted cuts to the heart of your argument. Getting the "right amount of air to the rooms with minimal leakage" generally requires testing "static pressure, airflow at the coil and room balance." It means focusing on "performance rather than products." It means that it's going to cost more than just throwing the flex in as quickly as you can.

I appreciate all your contributions here, David, so if you think I quoted you out of context or misinterpreted something, feel free to call me on it. I thought you were in favor of banning flex, and I was wrong about that here. Thanks for the clarification.

By: David Butler

David Butler — Mon, 29 Oct 2012 23:09:47 +0000

@Allison: I haven't changed
@Allison: I haven't changed my position on flex. You took that statement out of context. Here's what I said:

"I say the high performance building industry needs to focus on performance rather than products. Test the static pressure, airflow at the coil and room balance. If the system gets the right amount of air to the rooms with minimal leakage, then I don't give a rat's ass how they accomplished it. Programs that require Manual D submission are missing the point. Anyone can create a drawing."

And a follow-up...

"And by the way, getting flex right adds cost. Contractors will discover they may be able to install metal for less than flex, to achieve the airflow targets. Or at least the difference is much less. "

The fact is, room and system airflow verification is not happening in the vast majority of homes, and poorly installed flex is among the most serious impediments to achieving good performance. So yeah, I agree with John's point... "If you cannot get people to do it right, you should get rid of it." But as John said, it's not gonna happen.

Back to the real world: I routinely specify flex for runouts (thanks for pointing out the noise issue, Cameron). I find that contractors who install metal T&B; or extended plenum duct systems are much more likely to do a good job on the flex runouts.

By: Allison Bailes

Allison Bailes — Mon, 29 Oct 2012 22:35:06 +0000

Mike M.:
Mike M.: Yes, using flex only for straight runs would be best. Thanks for the link for the interesting paper on pressure drops in flex duct. I've just skimmed the paper but will dig into it later.

David B.: It seems that you've changed your opinion on flex, so I'd be interested in hearing more about that. In a comment to my article on whether flex duct should be banned, you wrote in April 2011, "If the system gets the right amount of air to the rooms with minimal leakage, then I don't give a rat's ass how they accomplished it." Do you really now think flex should be banned?

John P.: It seems to me that the problem isn't so much in the product as in the training and motivation of the installers. If you have the same people who are installing flex badly change to installing hard pipe, how much better will it be? I've seen bad hard pipe installs, too.

Jerry P.: That's a good question, but this article is about flex duct, not cellulose insulation in vaulted ceilings.

Cameron T.: I agree. Flex should be used more sparingly than it is, and it's great at reducing noise.

By: Cameron Taylor

Cameron Taylor — Mon, 29 Oct 2012 16:41:41 +0000

Flex duct was originally
Flex duct was originally intended to serve as terminal drops for hard duct trunks; IOW, the last six feet or so of duct to a register could be flex to improve sound attenuation and reduce overall installation cost.

Of course, human nature being what it is, I'm certain right after the product came out someone shrugged his shoulders and said "Why not just use it for the whole job?" And so it went...downhill from there.

I have modified all metal duct systems, that were so noisy when the AHU ran that the home occupants had to raise their voices to talk, with sections of flex to dampen the sound and eliminate cross-talk, with no loss of air delivery performance. Of course I combined that effort with adding jump ducts for return air, along with better supply registers. The system to this day works fine. All it takes is some thinking beyond "get 'r dun".

By: Jerry Pollard

Jerry Pollard — Sat, 20 Oct 2012 16:38:47 +0000

Question regarding dense pack
Question regarding dense pack cellulose...I have seen it used in slant ceilings, installed after sheetrock, back-filled. Is there evidence that this is "kosher", or is there risk of condensation because of air flow within the material?