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Can Power Vent water heater vent pipe run horizontal in an unconditioned attic?

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I am planning to replace my current natural draft water heater with a new high efficiency power vent unit.  Can I run the PVC vent pipe straight up into the attic and then horizontally to a side wall for termination?  There are no windows or doors on the side wall.  The attic space is unconditioned and will see extreme temps in the winter and summer.  The water heater will be a A.O. Smith GPHE-50.
asked in Plumbing by dnapier (120 points)
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1 Answer

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Hi DNapier,
Yes, you can install the water heater’s vent pipe vertically up into the attic and turn into a horizontal run through the side wall of the house. 
Based on the manual / recommendations for this particular model / scroll to literature section on the following page and download - http://www.hotwater.com/water-heaters/residential/conventional/gas/vertex/vertex%E2%84%A2-power-vent-50-gallon-gas-water-heater/
Attic consideration / hot summers: “For water heaters in locations with high ambient temperatures (above 100°F) it is recommended that CPVC or ABS pipe and fittings be used." Attic temps may reach way over 100°F during the summer. 
General for vent pipe installation: "All vent (exhaust) pipes must be pitched a minimum of a 1/4” per foot back to the water heater to allow drainage of condensation.
Hot summer will not affect the amount of condensation but low temperature will definitely increase its amount so make sure to monitor condensate disposal assembly periodically.
Just follow (or the installer) the instructions provided at the manual (number of elbows and pipe dimensions / lengths are extremely important) and you should be OK. Don’t forget to provide sufficient amount of combustion air if you choose to use single vent pipe installation / combustion air from interior!
There are many important suggestions in the manual so take your time while reading it.
answered by darekrudy (21,730 points)