Subject: Re: Layman question: Duct material

From: Doug Geddes <[email-masked]>
Date: 07 Oct 1995 02:34:53 GMT

>I've gotten two quotes for a heat pump system for a new 2200 ft2 ranch 
>house (ducts run in a crawlspace). Both have bid some kind of insulated, 
>foil-covered board for the ducts (by Certainteed). Wouldn't steel ducts 
>with insulation on the outside be better? The house is in an area where 
>animals may be a problem. 
>
>I guess I could see where the insulated board would be quieter than steel 
>ducts, but I also wonder how they would hold up over the years. I'm 
>considering a humidifier, and would that keep them too damp?
>
>Thanks for the help!
>
>-Mark Slone        [email-masked]
>
>
Hi Mark, good question.  I believe you cannot beat good old fashioned 
insulated metal ducts.  They don't fall apart and are vermin proof.  Having 
said that, we in Canada have never been stupid enough to put our ducts outside 
the building envelope - of course we all have basements which makes that a lot 
easier.  Grin.  There are a thousand good scientific reasons that all ductwork 
should be inside the house air/vapour barrier, but that is another issue.  If 
you must go outside and animals could be a problem, stick to metal, either 
rectangular or round ducts that are secured with sheet metal screws.

Regards from sunny Canada (never said warm, just sunny)
Doug

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From: [email-masked] (Matthew Klein)
Date: Sat, 07 Oct 1995 10:28:13 GMT

On 07 Oct 1995 02:34:53 GMT, Doug Geddes 

>considering a humidifier, and would that keep them too damp?

Ductboards, or fibrous glass ducts as they are properly called, are
gaining in popularity because a contractor can fabricate the ducts
on-site very easily, and they are cheaper than insulation-lined metal
ones.  The problems that I heard about these ducts so far is that
contractors are not installing them with adequate support and the
taped seam on some opens up.  I am not totally sold on them yet
because they are relatively new and not enough time-tested data exists
yet.

Humidity is more a problem in the cooling season than in the winter
when you would be humidifying.  During the cooling season, the
humidity of the air coming from the coil could be 100%.  The jury is
still out about whether this is conducive to mold growth inside the
ducts.  However, if you have an efficient filter system on the
furnace, you should not get the dust in the duct to serve as the mold
source and food.  Usually, humidifiers are mounted on the return duct
and should not be a problem unless you have a strange setup or the
humidifier messes up and allows water to saturate the ductboard liner.
In this case, I would be more concerned about the ductboard falling
apart.

A good way to judge how well the contractor knows how to use the
ductboard is to ask it if it has heard of the North American
Insulation Manufacturer's Society (NAIMA).  This trade society has
produced a standard, "Fibrous Glass Duct Construction Standard", that
details how the ducts are to be constructed and installed.  Make sure
that the contractor follows the standard.

Otherwise, I must agree with Doug that if the ductwork is outside of
the house in a crawl space, I would feel a lot better about it being
metal.  Who knows what kind of creatures will find habitat in that
area.  I had touble with rats getting into metal return ducts in the
crawlspace of an old house I once owned.  God only knows what the
little darlins would have done with fiberboard.
Matthew Klein, PE
Indoor Air Quality Solutions
513-734-7526
[email-masked]
*************************
Wouldn't it be nice if common sense was really common?