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.
- posted
16 years ago