Homemade Retangular HVAC Ducts

MEMPHIS91 · 06-16-15, 08:18 PM

Howdy guys I got a quick way to save some big bucks on redoing the old or putting in new duct work. I needed to replace an old undersized/under-insulated 8" round metal duct in my attic. It was trying to run 4 registers. So I priced some metal rectangular truck to come off my main plenum, 24 feet long 10" x 12" was a whooping $675! That's not even installed. So I started looking into what would be needed to do the job right. Here is what I came up with. $150 total cost.

Parts list (all from Home Depot)

Owens Corning FOAMULAR 3/4 in. x 4 ft. x 8 ft. R-4 Tongue and Groove Insulating Sheathing-37L - The Home Depot

GAF 0.5 in. x 4 ft. x 8 ft. EnergyGuard PolyIsocyanurate Insulation Sheathing-1S01 - The Home Depot

Master Flow Water Based Mastic Half Gallon Tub-WBA50 - The Home Depot

3M 17.6 oz. High-Strength 90 Spray Adhesive-90-24 - The Home Depot

So I took the foam boards to the table saw and cut my pieces out.

I cut the PolyIsocyanurate (with vapor barrier) smaller to be 3M spary glued to the FOAMULAR .

This is some crazy awesome stuff! Its water based too so it washes up really easy.

I the coated EVERY seem VERY well with the mastic and glued them together. I then came back and coated the outside of each seem as well.

All done. I just have to make up 2 more and replace the old with the new. This should give me a R valve of over 7. Finished inside size of 13" x 9".

Daox · 06-17-15, 07:41 AM

Hah, very nice!

I wonder how the mastic will hold up over the years though? I suppose that is pretty much what it is designed for...

MEMPHIS91 · 06-17-15, 09:35 AM

Thanks. It should last a long time. But foil tape will be added to all seems after installation.

MEMPHIS91 · 07-15-15, 09:52 PM

Got the ducts roughed in. Old 8" hard pipe = 160 CFM. New foam ducts = 600 cfm.

06-16-15, 08:18 PM	#1
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	Homemade Retangular HVAC Ducts Howdy guys I got a quick way to save some big bucks on redoing the old or putting in new duct work. I needed to replace an old undersized/under-insulated 8" round metal duct in my attic. It was trying to run 4 registers. So I priced some metal rectangular truck to come off my main plenum, 24 feet long 10" x 12" was a whooping $675! That's not even installed. So I started looking into what would be needed to do the job right. Here is what I came up with. $150 total cost. Parts list (all from Home Depot) Owens Corning FOAMULAR 3/4 in. x 4 ft. x 8 ft. R-4 Tongue and Groove Insulating Sheathing-37L - The Home Depot GAF 0.5 in. x 4 ft. x 8 ft. EnergyGuard PolyIsocyanurate Insulation Sheathing-1S01 - The Home Depot Master Flow Water Based Mastic Half Gallon Tub-WBA50 - The Home Depot 3M 17.6 oz. High-Strength 90 Spray Adhesive-90-24 - The Home Depot So I took the foam boards to the table saw and cut my pieces out. I cut the PolyIsocyanurate (with vapor barrier) smaller to be 3M spary glued to the FOAMULAR . This is some crazy awesome stuff! Its water based too so it washes up really easy. I the coated EVERY seem VERY well with the mastic and glued them together. I then came back and coated the outside of each seem as well. All done. I just have to make up 2 more and replace the old with the new. This should give me a R valve of over 7. Finished inside size of 13" x 9". Attached Thumbnails

06-17-15, 07:41 AM	#2
Daox Administrator Join Date: Aug 2008 Location: Germantown, WI Posts: 5,525 Thanks: 1,162 Thanked 374 Times in 305 Posts	Hah, very nice! I wonder how the mastic will hold up over the years though? I suppose that is pretty much what it is designed for... __________________ Current project - To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts. & To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

07-15-15, 09:52 PM	#4
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	Got the ducts roughed in. Old 8" hard pipe = 160 CFM. New foam ducts = 600 cfm. Attached Thumbnails

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06-17-15, 09:35 AM	#3
MEMPHIS91 Journeyman EcoRenovator Join Date: Apr 2015 Location: Oxford, MS USA Posts: 496 Thanks: 69 Thanked 87 Times in 61 Posts	Thanks. It should last a long time. But foil tape will be added to all seems after installation.