# vent size for 40 gal gas water heater



## gregzoll (Dec 25, 2006)

Would be easier to just go with a power vent water heater.


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## beenthere (Oct 11, 2008)

Nope. Just use the 3", and then when you get the larger water hear, run a new pipe of the proper size.


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## amakarevic (Apr 12, 2007)

beenthere said:


> Nope. Just use the 3", and then when you get the larger water hear, run a new pipe of the proper size.


but the pipe runs through a ceiling, i would have to tear off drywall. what's wrong with using a size bigger vent?

cause once it goes into the chimney shaft, it will be bigger anyway (6"). so what's the problem with being less bigger on its way there? there is about 10' of sloped horizontal piping between the appliance and the chimney.

also, this is type B venting.

e.g. i could use a 3" pipe to go directly out of the appliance to the ceiling where it makes the first bend. but then there it would meet a 3->4" adapter. does this sound OK?


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## beenthere (Oct 11, 2008)

6" vertical is ok. But a larger size horizontal will slow the flue gasses and give them too much time to cool. Specially the pilot flame. And generally cause poor draft problems, and condensate issues.

The max size chimney a 3" vent hood may be connect to is 49 sq in of area/cross section. a 6" round is only 28 sq in so thats ok. 

Is the B vent coming through the ceiling all vertical, or is any of it horizontal.


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## amakarevic (Apr 12, 2007)

beenthere said:


> Is the B vent coming through the ceiling all vertical, or is any of it horizontal.


there is about 10' horizontal between where it enters the ceiling above the appliance and the chimney. then about 16' vertical.


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## beenthere (Oct 11, 2008)

And you have 1" clearance for the B vent in this area above the ceiling?


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## amakarevic (Apr 12, 2007)

beenthere said:


> And you have 1" clearance for the B vent in this area above the ceiling?


absolutely, i actually have something like a sub-ceiling through which the pipe runs and there is AT LEAST 1" clearance everywhere around the pipe.


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## hvac122 (Dec 10, 2007)

Believe it or not here in Lincoln NE it is against code to run anything smaller than 4" off of a water heater. We must use a 3-4" increased right off the diverter or as quickly as possible. 
Inspectors know all. Lol


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## newtech (Mar 21, 2009)

Most building codes require 4-inch flue pipes on water heaters. 

I know that we have to here.


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## beenthere (Oct 11, 2008)

Not here. 3" if its a 3" breech.


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