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Old 10-19-2011, 01:39 PM   #1
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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

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Old 10-19-2011, 03:18 PM   #2
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vent size for 40 gal gas water heater


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

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Old 10-19-2011, 03:30 PM   #3
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vent size for 40 gal gas water heater


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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Old 10-19-2011, 03:40 PM   #4
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vent size for 40 gal gas water heater


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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?

Last edited by amakarevic; 10-19-2011 at 03:56 PM.
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Old 10-19-2011, 04:28 PM   #5
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vent size for 40 gal gas water heater


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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Old 10-19-2011, 04:33 PM   #6
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vent size for 40 gal gas water heater


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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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Old 10-19-2011, 04:35 PM   #7
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vent size for 40 gal gas water heater


And you have 1" clearance for the B vent in this area above the ceiling?
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Old 10-19-2011, 04:39 PM   #8
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vent size for 40 gal gas water heater


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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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Old 10-19-2011, 04:53 PM   #9
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vent size for 40 gal gas water heater


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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Old 10-19-2011, 05:26 PM   #10
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vent size for 40 gal gas water heater


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

I know that we have to here.
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Old 10-19-2011, 06:15 PM   #11
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vent size for 40 gal gas water heater


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

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