Flex Ducts

Michael Farha · 08-09-2010, 08:03 AM

Has anyone heard that flex duct will no longer be used in new construction in the near future? I got this from a HVAC tech yesterday. If yes, what are the reasons? Any info will be helpful.

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Elliot Franson · 08-09-2010, 08:28 AM

Originally Posted by Michael Farha

Has anyone heard that flex duct will no longer be used in new construction in the near future? I got this from a HVAC tech yesterday. If yes, what are the reasons? Any info will be helpful.

Mr. Farha:

I have not heard of this. Though I have become willing to believe nearly anything in the past few years, I doubt that this will come to pass in the near future.

**Gunnar Alquist** · 08-09-2010, 08:32 AM

News to me. Everybody uses flex out here. At least for residential. Probably use metal in commercial.

Ted Menelly · 08-09-2010, 08:37 AM

I actually did hear that but not sure how long ago or by whom. One of those things that just was kind of "Really, hm"

Elliot Franson · 08-09-2010, 11:35 AM

Here is a link to that information.

Mitsubishi CITY MULTI® Minisplits.

**Rod Butler** · 08-09-2010, 11:58 AM

Originally Posted by James Risley

They are probably talking about the Mitsubishi new "City Multi Heat Recovery" system. They provide heat and cool (simultainously) to individual room ceiling units. One room can heat and one room can cool at the same time. They use liquid lines from main unit to room units. NO DUCT required. Fresh air intake will have to be handled somehow.
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JR

huh?

Not sure what this has to do with flex duct . . . .

Flex duct is used extensively in residential AND commercial systems. Even high end HVAC system rely on flex duct to a certain extent. I would be amazed if codes eliminated the use.

The truth is flex duct when installed properly is a very good and useful product.

**Rod Butler** · 08-09-2010, 03:13 PM

Originally Posted by James Risley

This thread asked if flex duct was not to be used in the future. The answer is that with one of these minisplit systems there is no need for flex duct as the refrigerant goes from main unit to each room unit and NO DUCT is involved. You may, however, want to use flex duct to supply fresh air. I did not take the original post to say that flex duct was to be eliminated by code.......Possible I misread the original post.
JR

I made assumptions as well James, thanks for your clarification.

**Markus Keller** · 08-10-2010, 06:06 AM

If you see a lot of flex duct, you may want to check your Code. Length and type of flex duct is limited here. Forget the length 5' or 6' for the most part. Been a while since I read that section. The gray plastic outer sleeve flex duct is limited in use. The silver foil outer sleeve flex duct is Ok for more use. Something about fire/fumes with the gray plastic sleeve.
Hope that confuses the issue more.

**Darren Miller** · 08-10-2010, 07:07 AM

There are 2 different types of 'Flex'- one is a connector and one is a duct.

A flex connector is limited to 14 feet while a flex duct is unlimited.

**Jerry Peck** · 08-10-2010, 03:59 PM

Originally Posted by Darren Miller

There are 2 different types of 'Flex'- one is a connector and one is a duct.

A flex connector is limited to 14 feet while a flex duct is unlimited.

Correct.

One is simply an "air connector" and is not classified as a duct, with (as Darren said) a maximum allowed length of 14 feet. These are not insulated - basically think of these as flexible duct without the insulation or outer covering.

David Bell · 08-10-2010, 04:07 PM

Flex connectors may be insulated but may also be made of thin wired mylar internal tubes with mylar outer wraps that do not meet flame spread requirements for flex duct.