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Discussion Starter · #1 ·
I'm changing the 12" flexible duct running through my garage/HT conversion, to a duct made out of JM SuperDuct ductboard. I finally managed to source some in the Bay Area (General Insulation in Hayward), and they had a box of six slightly damaged sheets they let me take off their hands for free (I only need about three, so I can trim away the damaged areas). So far so good.


Now I am trying to source the tools to use with these, without paying a fortune. I'd love to rent, but failing that has anyone worked with ductboard and have any tricks or tips? Unfortunately, this will have to be inspected, so the tips and tricks will need to follow code.


One of the other things I am trying to figure out. I will have a 14" x 10" duct running inside a soffit. I wish to run a 10" x 4" take off using ductboard as well, running between the ceiling joists to a register. How do I interconnect ductboard to ductboard? I know how to extend them straight (using male/female shiplaps), but how do you make a corner, or takeoff? Also, how do I (or can I) connect a register directly to the ductboard?


Of all of the areas I have tried to DIY in, HVAC seems to be the most secretive. I have done plumbing, electrical, framing, concrete, drywall (all permitted and inspected), and for the most part, you just buy a book and follow the instructions (slight oversimplification;))! But DIY information for HVAC/Mechanical seems very difficult to come by. Does anyone know any good resources/books?



Thanks again everyone,
 

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I have installed some ductboard but not a lot. The only place that I put it is in attics that are unconditioned. Gennerally ductboard is used only as a supply/return trunk and not as a branch duct to supply air to a register. The Supply ducts coming off a ductboard trunk are insulated flexduct that are connected to a spin-in start collar. The trunks are made by making a V-shaped cut on the fiberglass side of the of the duct and then fold the duct untill the matting edges contact each other. The mating edges should be cut at 45 deg. angle and are sealed using a heat activated tape (a hobby iron should do the trick).


I prefer to use sheetmetal and then insulate it with a new product that is refered to as "DOUBLE BUBBLE." Basically it is plain old bubble wrap with foil on both sides.


Sheet metal is a better way to go because the inner surface is smooth, which means better air flow. The tools that are needed for sheetmetal work can be purchased at any home center or hardware store. All of the various fittings can also be obtained from the same place. Since the ducts are going into a conditioned space you do not need to insulate them.


With regards to having a 10"x4" duct between the joists, If this is for supply air you may not get the air flow that you are expecting. The best thing to do is to use a 5' or 6" flat oval duct to fit in the joist space. Avoid using a bare joist space for supply air at all costs.
 

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Discussion Starter · #3 ·
Thanks for the information.


I've reconsidered and I am going to use flex duct for the branch ducts. I wanted to use ductboard for the supply run to help reduce noise transmission through the ducts.


I'm running soffits around the outside of the room, so I'll run 6" flex duct through them instead.


Do you know a good source for the tools to cut the "v" groove?


Thanks again,
 

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I buy all of my tools from HVAC supply houses, but you might want to call around to some in your area and see if they would be willing to rent them to you.


BTW the edges are joined using a half lap joint. You should be able to get the cutter for this joint at the same place you get the v-groove cutter.


I think that Grainger might have what you need. Check out WWW.Grainger.com
 
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