Reusing plastic vents on a tankless replacement: what Ontario and BC regulators have said

The rule both regulators start from

The short answer: plastic vent must be ULC S636 certified, and the requirement bites at replacement.

TSSA's Fuels Safety advisory FS-101-07, first issued April 16, 2007 and revised April 7, 2014, says clause 8.9.6 of CSA B149.1 requires plastic vents to be certified to ULC S636, the standard for Type BH gas venting systems. It explains that the requirement followed investigated failures in existing plastic vents, mostly ABS pipe and fittings, including stress cracking and melting, which could create a carbon monoxide hazard.

The advisory gives a water heater example directly: when an existing water heater is replaced, the existing plastic venting must be completely replaced with a certified ULC S636 system. It is not retroactive; existing appliances and vents need no action until the appliance is replaced.

Technical Safety BC's plastic venting directive, issued May 20, 2011, takes the same approach for BC: new and replacement installations need ULC S636 certified vent installed to the manufacturer's certified instructions, and existing systems are left alone until the appliance is replaced.

The narrow exception

The short answer: inspect, replace the first five feet, and pass a pressure test.

Both documents allow the existing vent to stay only where full replacement is impossible or impractical, and only if:

1. the first 5 feet of vent downstream of the appliance is replaced with suitable ULC S636 certified vent;
2. a visual inspection finds the remaining vent in good working order (cracked or damaged vent can't be repaired);
3. a pressure test with air or inert gas at a minimum of 7 inches water column, positive or negative, not exceeding 2 psig, holds at least 75% of the test pressure for at least 5 minutes.

If the vent fails the test, the whole system must be replaced. In Ontario, TSSA treats this as a variance application with fees, a test report and a five-yearly re-inspection condition; its 2014 revision lists the fees, which may have changed since. In BC, the directive also says cellular core vent material is not accepted and must be replaced whenever the appliance is.

What has changed since

The short answer: newer code and standard editions, but no replacement guidance that we found.

Both documents cite older editions of CSA B149.1. Codes have moved on: Manitoba's January 2026 bulletin on the 2025 B149 series notes revised vent clearance tables, for example. The Standards Council of Canada listing shows ULC 636:2026 as the edition that supersedes ULC-S636-08. We found no revised TSSA advisory or BC directive replacing the documents above, so confirm with the regulator before relying on them.

Analysis: how venting should show up in your marketing

This section is TanklessNews.ca analysis, not regulatory advice.

• Quote venting as its own line. Homeowners compare tankless quotes on the headline price. A separate venting line, with a sentence explaining why old plastic vent is usually replaced, protects you from being undercut by a quote that quietly reuses it.
• Explain it on your website once, well. A short page on why vent replacement is part of a tankless conversion, linking the regulator's guidance, answers the question before the estimate visit.
• Use photos you own. If you show vent work, show your own jobs with dates. Never use photos that suggest a cracked ABS vent is acceptable.
• Don't promise a reuse. Whether a vent can stay depends on inspection and testing on the day. Ads that say "no vent replacement needed" set up a dispute.

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