Sheet Metal Journal, the insight - the information

For over 25 years, a number of furnace, boiler and water heater manufacturers have approved the use of various types of plastic vent for their appliances. Plastic venting systems were introduced in the late 1970s as early versions of condensing forced air furnaces began to become popular. As time passed, more and more appliances were approved with plastic venting. Most used ABS, PVC, and CPVC.

Then forward to the mid ‘80s, where a plastic material known as HTPV (high temperature plastic vent) sold under brand names such as Solvent. This material was approved for higher temperature, power vented appliances such as mid-efficiency boilers and gained wide industry acceptance.

Then things began to unravel. There were many failures— mostly cracking and joint failures. These failures led to a ban, recall and replacement program in 1994. The failures caused many to question the use of plastics for venting, but on lower temperature appliances the practice continued. For higher temperature condensing appliances other venting material such as AL29-4C have become popular.
There have recently been a growing number of reports of ABS venting system failures on higher temperature applications, most notably, power-vented water heaters (the plastic becomes brittle and can shatter). These are some of the reasons prompting the supplemental to the gas code.

The rules to remember for “BH Gas venting systems” and all venting systems in general are READ APPLIANCE LABEL for the following:

a) Category of appliance
b) Rated flue gas temperature
c) Rated vent pressure

Designers and installers are reminded that British Columbia and several other provinces have announced adoption dates for the 2007 Supplemental to the CSA-B149.1 Gas Code. To allow for ULCS636 certified products to be available in plastic, British Columbia will implement the change on July 1, 2007. Alberta will be effective January 1, 2007. At the national level the change immediately applies to all federal projects starting in the new year.

The supplemental includes two significant changes:

8.9.5 Venting Systems, or total vent run if less than 3ft (900 mm), that employ plastic vents shall be installed such that the first 3ft (900 mm) from appliance flue outlet is readily accessible for visual inspection.

8.9.6 Vents constructed using plastic shall be certified to ULC S636.
At this time only one manufacturer has their plastic (S636) product certified for venting use with all components labelled to comply. This plastic venting falls in two types based on discharge temperature: below 65°C (149°F) and below 90°C (194°F). In all other high-efficiency cases needing Type BH vent there are many manufacturers that produce AL29-4C corrosion-resistant venting systems.

At this time only one manufacturer has their plastic (S636) product certified for venting use with all components labelled to comply. This plastic venting falls in two types based on discharge temperature: below 65°C (149°F) and below 90°C (194°F). In all other high-efficiency cases needing Type BH vent there are many manufacturers that produce AL29-4C corrosion-resistant venting systems.

The venting systems serving Category II, Category III, Category IV, Direct-vent appliances and appliances with integral vents shall comply with Table 8.5 of the Code. Special BH venting systems need to be installed in accordance with terms of their listing. It is important for Installers to remember that where a conflict exists between a manufacturer’s installation instructions and the Code, such as saying schedule 40 ABS is acceptable, that the Code saying ULCS636 shall prevail. Therefore, any thermoplastic piping material used for venting must be certified for this application or use metal venting AL29-4C type. n