Bury dryer vent under patio?

I am replacing a deck with a poured concrete patio.
The problem is that my dryer vents under the deck.
Does any see a problem using standard rigid aluminum ducts to extend from my house out to the edge of the patio? I will be pouring concrete on top of the 4" rigid vent.
I have thought of using PVC instead, but I would expect that would be a hazard were the dust in the vent to ignite.
Missing the patio is not an option, since I would have to route the vent through several floor joists.
Any better ideas?
Thanks.
Rick
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It may not be so bad with a straight pipe with no joints, but at some point it had to come up from under the concrete right? It just has to have some buildup of lint over time. I see that as being a big problem at some point.
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The patio is raised, and the duct would be about two feet higher the surrounding ground level.
However, after hearing the comments here, I am going to go up through the ceiling and out the end of the attic. Total run: 25 feet, one 90 degree elbow in the attic.
Thanks to everyone for all the info.
Rick
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PVC should be safe... Temps should be low enough by that point. Just be sure that the pipe slopes downward with no upturns anyplace.
If you can turn 90' (or even 45') and make the run shorter, do that.
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two things:
(a). any kind of plastic will burn (given sufficient conditions - the circumstances which create those conditions are highly unpredictable). why chance it ? use metal ducting.
(b). wouldn't you want hot dryer exhaust gases to flow upwards out of the duct, vs. down a pipe ?
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Dr. Doom wrote:

Metal ducting under concrete means cast iron pipe! Certainly not aluminum sheet metal.
Very many plastics are fireproof. One of the earliest, Bakelite, for example.
PVC is flame-resistant and self-extinguishing. It will burn only if a flame is continuously applied and even then very reluctantly.
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Even concrete will burn under the right conditions. The chances of PVC burning are slim.

You don't want any moisture running back into the house or collecting in the pipe.
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RickM wrote:

I'd use PVC. It's cheaper. It will not burn and even if it did, it's under concrete!
If you pour concrete on aluminum ductwork you risk crushing the pipe - concrete is HEAVY.
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I have never seen this done before, but one thing I can add is that aluminum and concrete do not go well together. If you are going to install duct I would suggest the galvanized steel type. Something which is very solid and steel is 4" EMT which is available at an electrical supply company. EMT is approved for concrete encasement. The actual outside diameter is a little bigger than 4" so you may have a problem connecting to 4" duct. 3.5" EMT might be just right.
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the longer the run the slower the drying and more energy wasted espically when lint collects.
i would look into moving the dryer or taking the vent UP and vent ont the new concrete deck.
what your proposing will cause endless grief espically if its a long run or has any bends.....
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Water? Ants? Rodents? Birds? Bugs?
Other considerations.
Steve
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RickM wrote:

I have installed several dryer vents thru concrete with PVC pipe. Code in this area limits you to < 30' total run and no more than 180 degrees total in elbows. Less is better, straight is better, larger is better. No less than 4" pipe and, if needed, put in a clean out.
Many new homes have washer dryer areas in the middle of the home for convenience and a pvc pipe through the concrete can provide the shortests, straightest run to vent.
I have never seen this done, nor seen any specs for using aluminum in this situation, so I would avoid that for several reasons, including; strength, deterioration in contact with cement, and difficulty in maintaining proper slope. Make sure to have at least 3" of concrete above the pipe (vent). This may require burying it under the concrete rather than running it through the concrete.
--
Robert Allison
Rimshot, Inc.
  Click to see the full signature.
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PVC has a static problem and will hold lint better than metal. You do not want this.
Pipe bigger than 4" is not better. The larger diameter pipes will not allow for the velocity of the clothes dryer blower to get the exhaust of lint and moisture out.
Alisa LeSueur Cetified Dryer Exhaust Technician http://CleanYourOwnDryerVent.com
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CDET 14 wrote:

Static electricity? On a buried pipe? Outstanding!

"Certified Dryer Exhaust Technician"?
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As someone else said this is bad and probaly the dumbest Idea ive heard yet run the vent up higher on the wall but thats not the best, move the machine as that is the best how cold is your world and think of ice as you run the machine thru a metal pipe . As a certified whatever you don,t stop this Alisa then stay away from my machine also here Pvc is against code as if a fire starts in it it will spread Metal is all that is allowed now.
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jim wrote:

Then your code writers are morons. PVC will neither burn nor support combustion.
AMENDMENTS TO INTERNATIONAL RESIDENTIAL CODE
B. The International Residential Code adopted by reference in Section101.2, 2000 International Building Code, is hereby amended as follows: [...] Section G2437 (Clothes Dryer Exhaust) is amended by adding section G2437.5.3 to read as follows:
G2437.5.3 Under slab installation. Exhaust ducts for domestic clothes dryers shall be permitted to be constructed of schedule 40 PVC pipe provided that the installation complies with all of the following:
1. The duct shall be installed under a concrete slab poured on grade. 2. The underfloor trench in which the duct is installed shall be completely backfilled with sand or gravel. 3. The PVC duct shall extend not greater than one (1) inch above the interior concrete floor surface. 4. The joints of the PVC duct shall be solvent cemented.
http://www.cstx.gov/docs/residential_amendments.pdf
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