On common natural draft NG water heaters, I usually see 4" vent pipe, but I was looking at specs on a 40gal unit on the Ruun web site, and the chart shows 3" for residential sizes up to 60 gallons. Somewhere else I was reading that it is not a good idea to have oversize flue vents on gas appliances. I can see where oversize vents would also be an energy waster. Are a lot of people installing vents that are too large? Anyone know of a good reference for sizing vents.
flue pipe size for venting water heater
Aug 27, 2007
2 Replies
Often, it comes down to what the local inspection requirements are. Some cities won't permit 3" vent.
The draft hood bypasses most of the air around the heater in standby mode so I doubt that losses are significantly different for 3" or 4".
Jim
Locally, we can't use a 3" vent if the water heater is the only appliance on the chimney.
JK
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