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Author Topic: PVC AC ducts, will it work?  (Read 7347 times)
grantgoold
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« on: March 26, 2008, 09:52:24 PM »

I am considering using PVC 3" pipe as my AC ducts. Anyone have thoughts as to the pros and cons of using this product. I will have the pipe run down the middle of insulation.

Thanks

Grant
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Grant Goold
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Nick Badame Refrig/ACC
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« Reply #1 on: March 27, 2008, 12:22:31 AM »

Hi Grant,

There is no reason you couldn't use PVC.... Allthough, I would use SCH40 for the insulation value of the thicker side wall.

If using the thinner sidewall, just be sure to wrap it with insulation or you may end up with drips if installed in an unconditioned area.

Good Luck
Nick-
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« Reply #2 on: March 27, 2008, 05:51:39 AM »

Grant,
   Does the sq. in. area of the 3" PVC equal the specification of your AC unit?  If not, you will probably not be happy with it.  Jack
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« Reply #3 on: March 27, 2008, 07:00:51 AM »

The roof top ac's that I have seen have an opening that is approx 4 by4 or 16 sq in of air supply and a three inch pvc pipe has approx 7.06 sq in of supply.  If you ran one each direction you would be getting about 14 square inches of supply -- adding a small vent right at the bottom of the ac ( with a diffuser that can be controlled ) may give you enough air flow to avoid icing in the unit and if you had openings at different locations along the tubes you could have a pretty good set up. I think I might head toward ABS instead of PVC because of the design it would be easier to modify and you can glue it and have it hold without conventional connections much better. Also ABS has the core cells that may insulate better.

Just a thought

HTH

Melbo
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« Reply #4 on: March 27, 2008, 08:50:53 AM »

Hi Grant,

I'm under the impression that you will use the pvc for branch runs and not your Main Trunk. Right?

If not, then what Jack and others have said is correct. You won't have enough CFM in 3" pvc.

You would need a 12" round pipe to handle the CFM's of 2 RV units.

Nick-
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Dallas
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« Reply #5 on: March 27, 2008, 11:04:26 AM »

If the vents are going to be run down the roof in the insulation, why not consider using 29g galvanized, bent on a brake to make a "tophat" kind of shape.. the same as your tophat structure in the framing?
probably not any cheaper, but it will take up a lot less room, and you can have it any width and depth you need.
After all, 3" PVC on the inside is 4" on the outside... that's a lot of space to take up with a heating vent that is buried in insulation.

Just a thought.

Dallas

I am considering using PVC 3" pipe as my AC ducts. Anyone have thoughts as to the pros and cons of using this product. I will have the pipe run down the middle of insulation.

Thanks

Grant
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ktmossman
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« Reply #6 on: March 27, 2008, 12:01:36 PM »

WARNING: I will be the first to admit I don't know diddley about this topic, so this may be a very stupid question...

If you run A/C and/or heat (conditioned air) through a plastic pipe, wouldn't you build up quite a charge of static electricity?
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Sam 4106
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« Reply #7 on: March 27, 2008, 01:53:50 PM »

Hi Dallas,
Not that it matters in this case, because 3" PVC pipe is too small to be used as A/C ducts, but 3" PVC has an O.D. of 3.5" not 4", as you stated.
Thanks, Sam 4106
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« Reply #8 on: March 27, 2008, 04:55:20 PM »

WARNING: I will be the first to admit I don't know diddley about this topic, so this may be a very stupid question...

If you run A/C and/or heat (conditioned air) through a plastic pipe, wouldn't you build up quite a charge of static electricity?

Good Point!

I have seen this done, they ran a non insulated ground line through the length of the pipe and attached to a frame ground.(electronic bay)

This was done in a non-moving application though, and really have no information if it worked or was just someone's idea.  Huh

Cliff

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Dallas
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« Reply #9 on: March 27, 2008, 05:03:59 PM »

But the Joints will be 4"

Hi Dallas,
Not that it matters in this case, because 3" PVC pipe is too small to be used as A/C ducts, but 3" PVC has an O.D. of 3.5" not 4", as you stated.
Thanks, Sam 4106
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rcbishop
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« Reply #10 on: March 27, 2008, 05:35:04 PM »

Sam....ain't necessarily so..depends on the mfgr. and the  total cubic inches for outlet.  I have 2.5  inch i.d. running thru a chase (not PVC) the length of the coach,  on one side, with several outlets.  Not a choice I would normally make. Three inch would have been better, but chase space did not allow.  Coleman  basement unit.  System has been doing well for several years.

FWIW  Lips Sealed
RCB
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« Reply #11 on: April 04, 2008, 11:33:25 AM »

I thought about this thread as I walked through Home Depot today.  I noticed PVC and aluminum gutter downspot in 3"x4" that might work for you.  There were also various bends and other fitting available.

Len
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