Flexible ducting

[desert-rat]

Hi,
I am getting new ducts installed in my house. I was kinda thinking I would like metal as that to me seems like it would deliver the cleanest air. However, between the 2 contractors I talked to they acted like metal is so expensive (and like they don't do it often). I guess my question really is what do you think of the flexible duct. I think it is mylar on the inside, then fiberglass, then some sort of shining material like tin foil on top. Do these deliver clean air. Does the interior liner ever split so that you have fiberglass running through your ducts?
Thanks
Desert-rat

[parkercie]

As for using flex duct in a crawl space aplication, I would suggest against it. It doesn't hold up well. In attics, I tend to be a little more forgiving of it if it is only used on the branch duct. In other words, the main return and the supply trunk lines should be metal. As for your question about fiberglass getting into the duct work....the biggest danger there is when one of your namesakes or some other varmint gets a hold of it and chews through it. The contractors you spoke with are telling you the truth, all metal duct is much more expensive than flex. The labor time increases and the cost of metal is through the roof right now, but if you have the means to install it...metal is a much better choice. When getting estimates, you might ask the contractor if they have their own sheet metal shop. Contractors that actually have there own metal shop may be a little less expensive route to go.

[desert-rat]

Hi Parkercie,
I appreciate the info. I just want to have it done right with the correct materials. It is the air we are breathing all day and night long the last thing I want is something that is toxic.
Thanks again.
Desert-rat

[jcacdoc]

The main trunkline should be metal of coarse. The branch ducts do not need to be metal. Foil flex is standard to use and is pre insulated. There will be no difference in air flow provided the main duct is size properly and the branch ducting is with in 15 feet.if the foil flex branch is more the this it could become a problem. Note: this information can be found in every box of foil flex they buy. Good luck!

[pstu]

I do not believe there is any toxicity problem with using flex duct. This type is very widespread where I live in S.Texas and of all the possible toxins I have heard of in the home, fiberglass really is not one of them.

Glass is pretty inert, you don't want to get much into your nose or lungs, but my impresson is this is irritation potential only. If you were really concerned about fiberglass would you not be frantic about sealing between your ceiling and some attic insulation? A supply leak (which is common) would systematically pull air out of the house creating a negative pressure, and about 70% of the makeup air would be pulled from the attic. This is what I understand to be true, please correct me if wrong.

Best wishes -- Pstu

[kayjh]

Fibreglass fibres have definite negative implications for health. If you look at manufacturers recommendations for handling the product during installation they recommend a filter mask and careful washup after handling. Fibreglass fibres have been linked to lung problems so I would check carefully before putting anything in theat allows the air to come into contact with open fibreglass fibres.

I am having flexduct used in my attic installation but haven't been told that the insulation contains fibreglass on the INSIDE of the duct work, so I will be looking into this.

I was told that there would be a fibreglass board lining the inside of the stale air return duct and I've asked the contractor to find another product to insulate with (the inside insulation is to reduce noise).

I'm concerned about the product breaking down over the long term and getting into the air stream.

[tonys]

a LOT more break-out noise from flex-duct.

[pstu]

If at all possible could you please post a link to some of this research. I believe there have been contradictory stories going around and it is necessary to look at the quality and origin of the research. Need something to separate the wheat from the chaff. Thank you.

Regards -- Pstu

[kayjh]

Here are a few:

http://www.aecom.yu.edu/ehs/Industrial%20Hygiene/Fs_Fibergls.htm

http://www.atsdr.cdc.gov/DT/fibrous-glass.html

It is clear that occupational exposure to glass fibers (as well as asbestos, rock, slag, etc.) have a greater indication for health problems, my position is that there may not be safe levels of these materials and it is best to minimize any exposure.

Just my $0.02 worth.

kayjh

[psychometric]

Find out what the code in your area allows regarding flex. In CT, no more than 14' in a run, and it cannot be installed in a non accessible space. rodents like to chew into it in the winter for living qtrs. also, an 8" flex duct has a greater pressure loss than an 8" rigid metal duct. If they change metal duct with flex, they need to go up 1" on sizes to be equal. Other than that, flex is a good, tight selection.

[not a filter expert]

Once the duct is installed, there is no reason for it to split. You should be more concerned with the connections made with flex duct than what is between the two liners. http://www.atcoflex.com/ This company has flex duct designed for Mobile Homes, I don't think it's a problem with crawl spaces...keep in mind it is my narrow-minded Florida experience that passes on this information.

Metal duct? Not used in Florida unless it is in a commercial application. If someone tells me they want the best...they get JohnsMansville product...www.jm.com




Originally posted by desert-rat
Hi,
I am getting new ducts installed in my house. I was kinda thinking I would like metal as that to me seems like it would deliver the cleanest air. However, between the 2 contractors I talked to they acted like metal is so expensive (and like they don't do it often). I guess my question really is what do you think of the flexible duct. I think it is mylar on the inside, then fiberglass, then some sort of shining material like tin foil on top. Do these deliver clean air. Does the interior liner ever split so that you have fiberglass running through your ducts?
Thanks
Desert-rat

[pgrasso]

Hi desert-rat,

You seem very concerned about the air in your home. I'm just wondering what other indoor air quality issues you are addressing with your comfort system.

As I'm sure everyone here can tell you, there are a lot of new and exciting IAQ products on the market. Other than the ducts, are there any other specific features you are looking at with concerns to IAQ?

-Pete

[static regain]

round metal insulated on the outside is my vote..but millions of feet of flex is installed every year in homes and business...its safe, usefull, and practical in most applications. Your lungs will never know the difference. Maybe 13 cents of fan energy my be loss...but..the price of a dinner out would be more over the period of one year.

[wolfman32]

All metal is the way to go it may cost more and take a littile longer to put in but in the long run it will be worth it. I have been to houses where the customer has to lay something ove the register to keep the rats out!!! We put in all metal and that all if the customer wants flex my boss tells them to call someone else. In the long run you will be glad you did.