Plenum construction

[kevenc]

I have done some HVAC work, but not much, and I've never had to construct a plenum. I know you can buy one, but I'm way too cheap for that, plus it's fun doing my own stuff.

I've got galvanized sheet metal, and a 3' brake, so I know I could make my own plenum out of that. I have to make both an intake plenum and an exhaust plenum (just dumping it into the garage as my last post concluded) to a horizontal unit in my garage attic.

I imagine it would make sense to insulate the intake plenum since it's in the attic?

I've heard of something called duct board? This and some foil tape and/or mastic could work?

I could make it out of wood and insulate it with foam board?

Tips? Thanks guys, you've been a great help to me so far!

 

[MUDFORD]

With your brake, building the plenum will be easy. You'll need to come up with some liner though. It's usually sold in 4'x100' rolls. If you had to buy a whole roll, you would be cheaper to just buy a pre-made plenum. Duct board is easy also, but ideally you would use the special tools for cutting and making edges. The tools are expensive. Wood and foam board would work, just might not look that great.

 

[Bronson]

Sure, You could make one, but is it worth Your time?
Measure the outlet on the furnace, and figure the max height that will work for You and let a sheet metal shop do the dirty work.
they will glue the liner in and then You can cut the holes where You need for the ducts....Just My 2 cents....

 

[12ozd]

My furnace is in the attic, and the plenum is not insulated.
Then again it only goes about 4 feet from the furnace to (through) the wall.

 

[pseudorealityx]

If you aren't ducting it out, and your main is only a few feet, just use 16" flex.

 

[kevenc]

You'll need to come up with some liner though. It's usually sold in 4'x100' rolls.

Can I just use foam board as liner? Or is it hard to glue in?

 

[kevenc]

>Sure, You could make one, but is it worth Your time?

That's an interesting idea. I'll have to think about that if I can't come up with an easy way.

I tend to build everything myself, but I'm getting to the point where I should simplify. It would be nice to concentrate on things that I actually enjoy, rather than just to save money. I've only got so much time...

In this case though, I've never done it, so I feel that I should, mainly just to say I did ;-)

 

[kevenc]

Using large flex duct is a really interesting idea, but unless I can find a nice A/C shop nearby that uses flex duct, I'd have to buy 12', and throw away 8'...

 

[kevenc]

I just remembered I saved the plenum that I took off, so I have one really large plenum I could use as inlet or outlet if I so choose. I could cut it down too, it's way larger than it needs to be.

It's square, so I'm tempted to use it on the inlet and make a curved one for the outlet, but maybe that's just the engineer in me, since it's only going about 3' and dumping.