TL;DR
A Category IV vent is the venting classification for gas appliances that operate with positive vent pressure and condensing flue gases, the regime of modern 90-plus-percent furnaces and tankless water heaters, requiring sealed, corrosion-resistant pipe rather than metal flue. Because the appliance pushes acidic, water-laden exhaust below its dew point, the pipe must be gas-tight and pitched back toward the unit to drain condensate, with materials the manufacturer lists: PVC, CPVC, or polypropylene, and ULC S636-certified plastic in Canada.
What it means
A Category IV vent is the venting classification for gas appliances that operate with positive vent pressure and condensing flue gases, the regime of modern 90-plus-percent furnaces and tankless water heaters, requiring sealed, corrosion-resistant pipe rather than metal flue. Because the appliance pushes acidic, water-laden exhaust below its dew point, the pipe must be gas-tight and pitched back toward the unit to drain condensate, with materials the manufacturer lists: PVC, CPVC, or polypropylene, and ULC S636-certified plastic in Canada. Connecting such an appliance to an existing B-vent or masonry chimney destroys the chimney with acidic condensate and leaks flue gas at the seams.
Where it sits in the glossary
Category IV vent is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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