Fiberglass duct work

[never_retreat]

Anyone here ever work with that fiberglass duct board?
A guy a work with wants me to swap out his oil fired hot air furnace with a new gas one. The duct work is made of that stuff.
Any techniques or tricks? I only need to rebuild the two plenums, so I don't think its worth trying to adapt to metal.
FWI two different contractors wanted over 10 grand to do this job. The gas line is only 5' away outside, easy job.
I have not priced up the hardware yet but its not anywhere near that much. 105,000 btu's of heat Not sure about the tons of cooling existing but I'm going to go with 4 tons. The house is probably about 1800 sq ft plus a finished basement. Standard construction ranch circa 1985. I think that should be good.
There is vents in the basement but no return. I'm going to cut a return in for down there to balance the system a bit.
He also has a wood stove down there, is there any rules about how close to a wood stove you can put a return? I want to try and suck that heat in if possible.

[wmenorr67]

Paging 280plus.  Please pick up the white courtesy phone.

[280plus]

Sorry, 280 has left the building... 
Nota good idea putting a return in a basement with a woodstove. It may end up sucking smoke into the room and up into the rest of the house. Not to mention sucking up ooky basement smells if there are any.

4 tons actually sounds pretty big for 1800 sq ft. You need to do a good heat gain/loss survey to size things correctly.

Lots of tricks to fiberglass duct. The stuff sucks to begin with. If you haven't worked with it it'll be tough because you need to make flaps, staple them with an outward clenching staple gun and then tape them with silver tape which needs to be squeegee'd out. I can't recommend you go diving into this, you could wind up with big problems on your hands.

[Jim147]

I've worked with duct board a couple of times. But I had a guy with me that really knew how to fit it. They make a tool to cut out the bends. This guy could do it free hand.

If he can get an energy audit done before you do the job, he would be happier in the long term.

Check around and see if you have any dealers that will make sheet metal plenums to your specs and then tie them into what is there.

jim

[never_retreat]

4 tons actually sounds pretty big for 1800 sq ft. You need to do a good heat gain/loss survey to size things correctly.

Its a 1800 sq foot ranch plus the finished basement, thats not included in the 1800 sq ft. The basement is 90 percent finished and a walk out.

Nota good idea putting a return in a basement with a woodstove. It may end up sucking smoke into the room and up into the rest of the house. Not to mention sucking up ooky basement smells if there are any.

Again wood stove is in a finished basement. I will put the return low anyway so I don't think this is going to be a big problem.

Would you just lay out your folds on the sheet and cut out a v notch where you want to fold it? make a square and tape the loose edge.

[Nick1911]

Its a 1800 sq foot ranch plus the finished basement, thats not included in the 1800 sq ft. The basement is 90 percent finished and a walk out.

Understood, but basements generally don't have much of a cooling load.

You need to do a good heat gain/loss survey to size things correctly.

+1 to this.  Get someone in there to do a block load manual J calculation, if not a room by room.

I think duct board is a miserable material to work with and a poor solution to the problem at hand comared to sheet metal.  I personally avoid it if I can and recommend everyone else do the same.

[280plus]

Again wood stove is in a finished basement. I will put the return low anyway so I don't think this is going to be a big problem.

I do believe it it would be against code but I'd want to double check that before I say it is. I do not believe you are supposed to return from the same space combustion is taking place. I know you can't return from the space the furnace is in. Not sure how that applies to wood stoves. I'd check with your local building official. Call him (or her) up and tell them you're thinking about putting a return in the basement where there is a woodstove. Is that ok?  We're talking about carbon monoxide poisoning here, so don't take it lightly please. It may be perfectly fine. I'd have to spend time I don't have right now researching it. So it is in everybody's best interests that you do the research yourself before you forge ahead.

On the subject of fiberboard, What Nick said ^^^

I've been in this business 30+ years. if it was me the fiberglass would go away where I needed to rework the duct and sheetmetal would take it's place. Guaranteed the fiberboard will be falling apart in 5 years if you go that route. My gut feeling is if you don't do this kind of work for a living you are really stepping off into uncharted territory that could get you in a lot of trouble one way or another down the road. Or at the very least a pissed off friend. It really does take a lot of experience to get it all right. That's what the $10,000 is all about. IMHO that's the best advice I can give you in this particular situation.

[never_retreat]

I may just skip the fiberboard and use steel, that I can handle.
Somewhere I have a book on figuring out the heating and cooling load. I will have to find it and take measurements at the house.
There is not much I can do about duct sizing, I only have a few feet of the trunk expose till it goes into a finished ceiling in the basement. So I won't be changing much of anything, mostly just the 2 chunks going up.

[280plus]

If you install metal it will require flexible connectors or "flex connectors".