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Can I build hot air ducts out of plywood?

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Kolesar Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Dec-14-07 06:20 AM
Original message
Can I build hot air ducts out of plywood?
The upstairs bedroom of this house has the heat register in the wrong place. It is out by the hall, and since there is no cold air return in the room, the heated air just leaves the room.

I have come up with an idea to shunt the heat along the back wall of a closet through a custom ductwork and have it pour out into the middle of the room (through a new register). The scheme would involve turning at some oblique angles that no off-the-shelf sheet metal duct would make. I was thinking of building my own duct work out of plywood. I could design some gentle gradual turns into it to minimize turbulence.

I would want to find some 50 year caulk to seal the joints and the transition from the existing sheet metal. Is there any temperature or safety reason not to do this? Thanks.
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Whoa_Nelly Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Dec-14-07 08:29 AM
Response to Original message
1. I don't think the wood would take very well with the expansion and contraction
that consistently happens with the heat being off and on and off again.

That's why sheet metal, or specific ductwork piping works well for the function you are describing: it can take the expansion/contraction without the swelling and distortion wood would experience as the metal is flexible and tight, whereas the wood is porous and unpredictable.

I would say: No, don't use wood.

Also, you mention oblique angles and moving heat.
Get a contractor.
Have it done right the first time, and have it be up to safety code.

Also
You may learn some more here with these free articles re: HVAC, especially using the newer more flexible materials for ductwork.
http://www.prospex.us/home-inspection-hvac.php





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Stinky The Clown Donating Member (1000+ posts) Send PM | Profile | Ignore Fri Dec-14-07 09:10 AM
Response to Original message
2. Do NOT use wood
It violates every code in the world and it can get moldy inside.

There are many kinds of flex duct, some with insulation, that can turn any corner you have. There is also rigid duct that can turn any corner you have. It uses commonly available sections. Home Depot/Lowes carries most of thew common stuff.



These are endlessly adjustable. Two used together will turn ***any*** corner.



There are also transition pieces to connect round to flat ductwork.
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Warpy Donating Member (1000+ posts) Send PM | Profile | Ignore Mon Dec-17-07 11:46 AM
Response to Original message
3. Do NOT use wood
Besides the mold and expansion problems, plus violating codes, over time it becomes a severe fire hazard as heated air dries it out.

If you want cheap and dirty, use gutter pipe or dryer exhaust tubing. Just make it METAL, and wrap some insulation around it.
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Kolesar Donating Member (1000+ posts) Send PM | Profile | Ignore Tue Jan-01-08 07:50 PM
Response to Original message
4. How I spent my five day holiday
Pounding, cussing, gluing, huffing,
Sawing, drawing, drinking, yawning
Crawling, squatting, lifting, climbing
Measuring, questioning, shopping, drywalling

I went with sheet metal and rivets. In the ductwork section of Lowe's, they sell this stout tool for bending metal without a sheet metal brake. It looks like a heavy duty ruler make of two pieces of steel. Along each edge, there is a narrow slot that you can push a piece of sheet metal into. One slot is an inch deep, the other slot is 3/8 inches deep. You put the sheet metal into the slot, lay the workpiece down on the workbench, then turn the tool up while pushing the slot edge down on the workbench. The tool can make a neat turn of up to 180 degrees.

I made this design on paper of four pieces of sheet steel that can make a transition from 3.5 x 10 inch duct to a 5.5 x 6 inch opening that fit the grill that we bought. Two of the pieces were aligned with two sides of the duct, so I could make all the calculations using the Pythagorean Theorem: h = sqrt (x^2 + y^2).

Many pop rivets and too much reaming and I had a very strong and stout part.

And the bedroom is now a decent temperature instead of being oddly cold and uncomfortable.
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NMDemDist2 Donating Member (1000+ posts) Send PM | Profile | Ignore Tue Jan-01-08 07:52 PM
Response to Reply #4
5. congrats, but sorry it took your whole vacation
well done!

:yourock:
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Kolesar Donating Member (1000+ posts) Send PM | Profile | Ignore Tue Jan-01-08 08:12 PM
Response to Reply #5
6. Thanks!
Happy New Year :party:
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Warpy Donating Member (1000+ posts) Send PM | Profile | Ignore Thu Jan-03-08 03:12 PM
Response to Reply #4
7. Doing the job correctly the first time
saves a lot of repairs down the line. Congratulations on doing just that.
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