Putting Duct Board in a Return Closet

[structuralengr89]

I am a structural engineer and was wondering if I can get some advice from one of you MEs.

I have an old house...like 100+ years old...it is 1 story, on a crawlspace with the HVAC unit in the attic. At some point HVAC was installed and the return was created from an old closet.

When we bought the house a few years ago, I was concerned with the return closet pulling air from under our house...(the house is/was very dusty) as the return was just open studs and the floor of the return was oak flooring with gaps in it.

About 2 years ago I applied mastic to all surfaces of the return closet. The mastic on the floor is now cracked due to the wood floors shrinking and expanding.

So I went and purchased a few sheets of 4'X10' duct board from an HVAC supply store and wanted to install it in the return closet.

QUESTION: If I install it with the FOIL SIDE TO THE INSIDE, will I get condensation between the insulation and the stud wall?

At the ceiling of the return closet there is a box built with duct board and the foil is on the outside. So there would be a transition point where the foil would be on the inside and then switches to outside as it goes in the attic.

My thoughts were that the air temperature in the return and stud wall would be about the same, until it got to the attic. I am in the deep south, so the attic might be at 120F and the Return air in the 70s.

I could put the foil outside and let it face the stud walls, but then I couldn't tape and seal it with mastic. Also, the inside face of the new duct board looks like it has a black painted surface (not very thick) and it looks like insulation from the duct board would be pulled through the return and into my house?

I am sure there are some code issues with this, but I am more concerned with air quality for my family

Thank you!!!!

 

[berkshire]

Structuralengr89
If I install it with the FOIL SIDE TO THE INSIDE, will I get condensation between the insulation and the stud wall?

The answer is yes , in Florida, South Georgia, Alabama, Mississippi and parts of Texas.

You need to check with your local building codes. Most codes do not allow return ducts made from wood or drywall construction materials any more. Although it was permitted in some states in the past. Some, but very few, state codes will allow an inward foil faced duct board in a dry climate under a stage type return closet, on a concrete floor with a vapor barrier placed down first, in a retrofit , where the air handler sits on the stage directly above, where in the past the stage would be made over bare concrete. But for the most part the foil must be facing out because if you do not, in high humidity areas, moisture can and will condense on the foil side from the outside, and cause the adhesive to let the insulation go. The building code I have attached is for California. This may be a little more stringent than some states, but they will follow along similar lines.
B.E.

You are judged not by what you know, but by what you can do.

 

[structuralengr89]

Thanks for the info and building code!

If I attached the duct board to the walls of the closet with the foil OUTSIDE, I guess I won't be able to seal it? I thought about spraying some contact cement adhesive to the walls (3 of the walls are old plaster and one wall is framed 2x material and plywood). I would cut off the gas to the home before doing this!

My main concern is the fiberglass in the duct board being released in the house (my supply lines are all metal). The black stuff on the inside of the duct board doesn't look very thick. Can I spray some black paint or something on there so the fiberglass doesn't come off?

I know this doesn't meet code!!!
Thanks again!

 

[berkshire]

The black stuff is a surface sealant to prevent loose fibers drifting on the air. A quick vacuum clean will pick up any strays , and your system filter should pick up the rest. on commissioning run the system for an hour change the filter and toss the old one.
See if this attached data sheet is for the same type of ducting that you bought.

You are judged not by what you know, but by what you can do.

 

[structuralengr89]

It has a red sticker on it that says:

1" Thick Type 475
c UL US Listed
MH-12358
Class 1 form A
Issue# F-570
Max Velocity 5000 fpm
Litho in USA


Our filters are 2~18x24s that are in the hallway grill before the return/duct board...So I'm guessing after installing the duct board, it would initially blow a bit of insulation in the house when I turn the unit on and then stop?

Thanks for your help on this!

 

[berkshire]

structuralengr89 (Structural) (OP)

Most heater / air conditioner air handling units have a last ditch air filter inside the unit, to stop this kind of thing.
I am going to suggest that you contact a local heating and ventilating Pro who can look at your system, and give you a quick assessment of what you need to do to comply with your local codes. A few dollars spent in this manner can save the expense of tearing out improperly installed Improvements later .
Your questions are along the line of " Do I need a diagonal brace on this or can I get away without one?" and the answer of course is " It depends."
B.E.

You are judged not by what you know, but by what you can do.

 

[structuralengr89]

I agree!!! I will take your advice (em..and what my wife has been suggesting) and get someone to take a look at it. I did get in the attic and look at the horizontal furnace and there is not filter in it. I saw where it would go, but whoever installed it, boxed the end where you can't put one in it. I am going to call someone and see if they can put one of those big Honeywell filters at the intake end of the furnace.

Your help is greatly appreciated!

 

[structuralengr89]

Photo Attached

 

[dbill74]

structuralengr89 (Structural) (OP)

If I'm understanding your situation, the closet turned return air (RA) plenum is in the middle of the house and goes floor to ceiling. In which case you would have been fine lining it with gypsum board, with duct board on the floor as a precaution. Insulating the walls of the closet isn't needed since the temperature difference between the air in the closet and in the rest of the house will be minimal, as such condensation is a non-issue. But you've got it so don't worry about it.

The foil lining on the duct board is a vapor barrier intended to keep moisture out of the insulation material which is very porous and if moisture laden attracts mold. Most condensation problems with ductwork occur on the outside of the duct, so you want the foil side facing out. Regarding condensation in the attic; unless you plan to keep your house at 60 or below in the middle of summer, don't worry about it, won't be an issue.

If you haven't looked into it further or gotten someone out, your filter is in the Lennox PureAir Filter box. This box includes your filters, UV lights and who knows what else to clean your air. I recommend finding a model number and downloading the manual from

http://www.lennox.com.

The filters in the grille are redundant, when they get dirty, take them out and no need to replace (unless you decide to get rid of the Lennox PureAir). You should also start replacing the filters in the Lennox PureAir box.

In most residences there is no mixing with outside air, relying on doors opening/closing to get fresh air in the house. In your picture, you claim attic air is entering through slots on the side. The unit looks like it could have a gas fired burner section, for which these slots are most likely combustion air intake.

Bill

 

[chicopee]

I personally would rather install a galvanized metal duct for the return line. It has less frictional resistance and will not damage easily if you decide to use the extra space in the closet.