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Old 02-10-2010, 10:12 PM   #1
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Question regarding installation in apartment

I have a question. I live in an 1 bedroom apartment, 4 small rooms, in a prewar apartment building. A year and a half ago they installed a Goodman GKS9 gas furnace with a CAPF cased indoor coil on top. Out of the unit comes six 6”wide ducts that go into each room of the apartment. The distances of the ducts are from 5feet to 10feet. The return air duct is in our hallway, approximately 2x2x2. There is an air filter behind the removable grate. Inside there is a stainless steel duct connecting the air filter to the Goodman unit where the fan resides. Lining this duct is 1” thick acoustic fiberglass duct liner. This unit I have on almost all the time. The problem is that in the 6 months I have been living here, I have been noticing black “dust” EVERYWHERE.

My girlfriend and I ended up cleaning up this black “dust” everyday due to the incredible accumulation. Wipe the bathroom counter clean, and by night there’s another layer. We examind the black dust under a microscope and saw that is consisted of black, red, and clear glassy fiborous hairs. They were all over the apartment.

Not making any sense to me, I opened grate to the return air duct, and took off the air filter. I saw that the installers had lined the duct with acoustic fiberglass duct liner and that all edges of this liner were exposed, the grey looking fiberglass in the middle of the two protective layers was showing. Putting two and two together I realized that the black dust we were cleaning everyday was fiberglass. We have done numerous tests to confirm that the black dust is in fact the fiberglass being sucked out of the acoustic liner from the open edges. We have contacted the contractor to express our concerns and he basically blew us off saying it’s standard material used, and no problem with the way it’s installed.

This gets to the crux of my question. I am not educated in the field of heating and ductwork installations, but this is what I have been able to surmise thus far:

1) calling the goodman company, I was informed that the furnace fan runs at 1200CFM

2) I calculated that 1200 CFM = 6111 FPM for the 6” ducts used in our apartment

3) the NAIMA requires that anything over 4000 FPM requires metal nosing on upstream edges of insulation (not done in our case, no edges were sealed at all, insulation being exposed at all edges)

4) that 6000 FPM is the MAXIMUM velocity allowed for this type of insulation material

Is the fact that on its face the FPM is 6111 mean that particular acoustic fiberglass lining should not have been used at all?

Secondly, isn’t it correct that at the very least, being that the FPM is 6111 or so, and 4000FPM being the guidline number, that all exposed edges of the fiberglass lining should have been sealed with foil tape, metal nosing, or something?

Did I even convert the 1200CFM to 6111FPM correctly?

Any help with these questions would be appreciated.

Jason W.


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Old 02-10-2010, 11:45 PM   #2
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You did it wrong.
You would have to know how many CFM each pipe is moving.
If you just use 200 CFM per pipe(1200CFM divided by 6). Then the FPM would be 1019 for each of the supplies.

The 2'X2' return duct would be 300FPM at 1200 CFM.

Doubt your moving anywhere near 1200 CFM. Thats just the rating of the blower on ideal duct work.
And with only 6-6" supply runs. You have far from ideal duct work.

What air filter are you using. Hope not a 3M filtrete.


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