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Understanding Improvements to Certified PVC Flue Gas Ventilation

Ask This Old House plumbing and HVAC expert Richard Trethewey explains why standard DWV PVC should not be used to vent gas appliances and what should be used instead.

What to Know About Certified PVC Flue Gas Ventilation:

  1. Gas appliances create flue products which include temperature, carbon monoxide, and sometimes moisture. These need to be vented outside to prevent poisoning (from CO), mold, and mildew.
  2. As appliances have become more efficient, traditional venting gave way to direct venting outside. This made venting with metal pipes obsolete, since eventually they would rust due to the moisture buildup.
  3. For years, contractors vented flue products with the same PVC pipes they use for liquid waste. This is no good because these PVC pipes can’t withstand the heat that comes out of gas appliances, so eventually they fail and crack.
  4. UL1738 code requires that PVC flue gas vent pipes and fittings must come from the same manufacturer (to ensure a tight fit) and they must be rated for venting.


Richard demonstrated vent piping from IPEX.