plenum


Anybody ever heard of or done an HVAC plenum in plywood? Would/could it work???
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I can't even begin to imagine that it would meet fire-safety codes...
--
Regards,
Doug Miller (alphageek at milmac dot com)
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On Mon, 31 Jul 2006 22:03:50 -0400, "Tim Taylor"

Why? Constant hot air flow & THIN wood?
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For AC it might work. For heat? Forget it.
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Yea, that's what I was talking about, just air. He's got electric heat. It's just in a garage, and was tossing around the idea of just a plenum box and about 20 feet of ductwork to say. It would be at the back of the garage on the ceiling just something to distribute the air a little more evenly. Metal is no big deal, but he's got about 50 sheets of plywood laying around and was just asking me. I don't have a clue as I did mine in metal since it's heat and air. That's why I wanted to ask here. Didn't mean to get the code police after me and to ruffle any feathers.
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Tim,
Something your friend may want to consider is the possibility of mold growing on the inside of that plenum. Unless it's coated, the wood will absorb moisture and he will have the potential for some bad mold problems.
Bob S.

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Bob, you know that's something I never thought of!! That's why I wanted some others thoughts on the matter. It's like looking for something dropped in the grass, extra pairs of eyes are always helpful! Thanks so much!!! And thanks everybody else!! Metal it'll be.
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I can't see where moisture or mold would be a problem. The air is dry, cold, and that alone should keep things free of mold. I would not hesitate to use plywood as a AC only plenum. I might paint or some other water based coating for the inside but that is just to keep things clean on the inside.
On the plus side you don't need to insulate the plenum as much (if at all) if it is made of plywood.
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<snip>

You don't think that there would be any condensation issues?
Molds seem to grow easily in many systems, if the HVAC folks are telling any truths...
Patriarch, thinking the metal isn't terribly expensive...
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Metal is not cheap. Have you seen the price of copper lately? Go check out copper wire at HD or Lowes.
When I put a furnace in my house it cost as much for the ductwork as it did for the furnace and the furnace was very expensive. I did all the labor installing the ductwork and furnace.
Condensation? There shouldn't be any. If you get condensation with wood then the condensation with metal would be worse. Wood is an insulator and metal a conductor.
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The duct tubing in my CALIFORNIA home is aluminum, or galvanized steel. An insulating blanket is wrapped around it.
I realize that we're different here in the Bay Area, and folks do things their own way elsewhere. Copper, though, would be pretty 'special'. The local newsies have run stories about lowlifes stealing copper from construction sites for the recycling cash. And some fool tries to strip a power junction box, getting partway before something struck him...
Nope. No copper here. YMMV.
Patriarch
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all metals have gone up in price. Copper is 4 times what it used to be a year or so ago. Aluminum, zinc, steel and more have had increases too. I looked at some copper tubing at Lowes two weeks ago. It was close to $5.00 per foot! A machinist across town told me that alumunim has had similar increases. Steel and zinc and the rest are starting to go up too.
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wrote:

If it is just for distribution and the duct is in the conditioned air area, that is, it is not going through your attic or other unconditioned area it would be fine.
My kitchen uses the soffit above the cabinets for distribution only, with three registers. But it is in the insulated, conditioned air area, so it works just fine. it is fed from the attic area by insulated metal duct.
Frank
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The air return in my old house was hardboard nailed between floor joists. Plywood should be fine for A/C or return.
Tim Taylor wrote:

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Tim,
Read the 'answers' to date . . . a lot of validity . . . HOWEVER . . .
Half of my basement is finished {NO - I didn't do it - crappy idea and crappy work}and the duct from the heater is 'covered' {boxed in}with the wood paneling. When we bought the house it was gas-fired hot-air HEAT ONLY. Later we replaced the old heater with a newer Heat & AC unit.
I am now in the process of 're-furbishing' out up-stairs bathroom. While the 'air out' grill is about a 4 x 11 inch rectangle, the ducting that feeds it seems to be a 4in circular 'pipe'. For I don't know how many reasons {'paranoid' being one}, I wouldn't want a 'hot air' duct of thin wood ONLY. Some 'el cheapo' insulated 'Dryer Duct' - even the flexible kind - would do for the actual 'transfer conduit'. It could then be 'disguised or 'supported' by the plywood.
Regards & Good Luck, Ron Magen backyard Boatshop

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