Anybody know how to make residential ductwork?

[buckeyefarmer]

The acceptable method these days for design is ACCA manual J (load analysis room by room) and Manual D (duct design based on manual J load analysis), assuming the AH was sized correctly with manual S. Almost anything will work, but not well.

 

[dex3361]

I bought my metal duct work in rectangular sections that were L shaped and snapped together. Then you used the tab tool to make the lips for the drives. I didn't use or need a brake and it was not expensive. The hardest part was making the adapted off of the air handler. :thumbsup:

 

[crbr]

Interesting thread.

 

[wedge40]

Just my :2cents:.
The guy who built my house cut corners where ever he could. So my crawl space in 8" under the joist and 16" if you're crawling between them. I have a short run of the fiber board and then all my run from there are flex duct. Since the crawl space is so small the flex duct touches the ground in plenty of place. Mice get in the crawl space and chew through the flex duct. Then make nests in there. I've kept them out of the house by covering all the vents with metal screen. Bottom line if you use flex duct make sure there is no way for rodents to get access.
Some day I'd like to either excavate the crawl space or jack the house up and then put metal duct in.

Wedge

 

[rtimgray]

I'm building this addition as a slab on grade, so I won't have to worry about crawl space issues. It is also a two-story, with the 2nd story under roof, so there is basically no attic. The ductwork will have to run inside a closet/chase area that is central in the addition. The branch lines will have to run in the space between the floor joists.

It is the above considerations as to why I am worrying over this ductwork issue now (we are going to pour footings for the addition in a couple of days from now. I've gotten the unit sized from a couple of different sources, and it comes out the same no matter which way it goes.

Thanks for the advice, guys.

 

[Powerstroke777]

Hello there. As a HVAC tech i can tell you that its no fun to "knock tin". whenever possible i use flex duct. its usually not as neat of an installation as metal duct but serves its purpose well. however after reading about your construction details, you really have no other choice than to use metal ducts. its the only material I'm aware of that can be placed in walls and ceilings that will give you the airflow and static pressure that you need. you could use duct board but in my experience the stuff seems to fall apart after a while. not to mention that it tends to collect mold and allergens and distribute them all over the house. plus a lot of duct cleaning companies will not clean them. as mentioned before your best bet is to find a fab shop to knock out what you need. most of them will install as well for a very reasonable price. most importantly do not cut corners on the insulation. the last thing you want is a sweating duct in your wall making your sheetrock moldy. I'm glad to hear you are sizing your ducts its a fatal mistake a lot of DIYers make. good luck!

 

[rtimgray]

your best bet is to find a fab shop to knock out what you need. most of them will install as well for a very reasonable price. !

This is the whole reason that I'm looking to fabricate my own ductwork - I don't feel that the prices that I've gotten in the past are even remotely reasonable - they have cost more than the unit and the branch lines. Plus, if I fabricate my own, I can work on it at my pace as I'm working on the framing in the house. It's really hard (impossible, so far) to get any HVAC suppliers interested in looking at a job now when the installation won't happen for another year (I'm not real fast when it comes to building). I really appreciate the advice that you and others have been giving me.

Good luck and take care.