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amakarevic 10-19-2011 01:39 PM

vent size for 40 gal gas water heater
 
my water heater has a 3" vent opening on top but i would like to use 4" vents from the heater to where it enters the vertical chimney part (which is a sleeve 6" inside the shaft) to enable future scaling up to maybe a 60 gal heater. i was wondering if using a size bigger vent would be OK for the time being.

thanks

here is the heater:

http://www.lowes.com/webapp/wcs/stor...AID=1023733042

gregzoll 10-19-2011 03:18 PM

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

beenthere 10-19-2011 03:30 PM

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

amakarevic 10-19-2011 03:40 PM

Quote:

Originally Posted by beenthere (Post 752145)
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?

beenthere 10-19-2011 04:28 PM

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.

amakarevic 10-19-2011 04:33 PM

Quote:

Originally Posted by beenthere (Post 752194)
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.

beenthere 10-19-2011 04:35 PM

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

amakarevic 10-19-2011 04:39 PM

Quote:

Originally Posted by beenthere (Post 752202)
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.

hvac122 10-19-2011 04:53 PM

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

newtech 10-19-2011 05:26 PM

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

I know that we have to here.

beenthere 10-19-2011 06:15 PM

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


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