Why UL-1738?

Why did Centrotherm seek and obtain ULC-S636 and UL-1738 product listings?

In the United States, Centrotherm obtained the UL-1738 listing for its InnoFlue® Polypropylene Vent Systems at substantial cost even though current national building code does not require it. It is Centrotherm's belief that life safety products should meet the applicable safety standard.  In 2017, National Fire Protection Agency (NFPA) added language to the 2018 national fuel gas code in support of utilizing UL-1738 listed flue gas vent systems for category II and IV appliances. This demonstrates the growing acceptance of the UL-1738 safety standard. InnoFlue is tested by Intertek and listed to UL-1738.

Why can’t the United States use the Canadian Standard, ULC-S636?

Current US building code is written around the UL-1738 safety standard. This would mean that U.S. code writing bodies such as NFPA, IAPMO, and ICC, as well as state and local jurisdictions, would need to re-write their codes or recognize codes of non U.S. based agencies / countries. 

What standards do original heating equipment manufacturers’ use to specify vent materials in their Installation and Operations Manuals?

In the US market, there are presently 4 standards called out by equipment manufacturers to define allowable vent materials for category IV appliances.
  • UL-1738 – US Standard for Venting Systems for Gas-Burning Appliances Categories II, III, and IV
  • ULC-S636 – Canadian Standard for Type BH Gas Venting Systems
  • ASTM D1785 –Standard Specification for Poly(Vinyle Chloride) (PVC) Plastic Pipe, Schedules 40, 80 and 120
  • ASTM F441 - Standard Specification for Chlorinated Poly(Vinyl Chloride) (CPVC) Plastic Pipe, Schedules 40 and 80
The ASTM standards referenced are for water and irrigation systems and are not for venting gases created by combustion. Charlotte Pipe clearly states in its technical manual: Furthermore, several of the ASTM standards applicable to plastic pipe and fittings that Charlotte Pipe manufactures include the following note: This standard specification does not include requirements for pipe and fittings intended to be used to vent combustion gases.

UL-1738 and ULC-S636 are both vent standards for the USA and Canada, respectively. The UL-1738 listing is considered the more stringent or difficult test to achieve. Additionally, there are several tests not performed under the ULC-S636 that are performed for UL-1738. The notable differences are as follows:
  • Pressure Testing: UL-1738 tests the system at 250% of rated operating pressure. ULC-S636 does not have a pressure test requirement.
  • Leakage Testing: The ULC-S636 leakage test (.3 L/H Max @ 100 Pa) is performed at a pressure 24% below the pressure utilized in the test for UL-1738
  • Low Temperature Handling Testing: UL-1738 has a drop test performed at -20⁰C, requiring no shatter, no chip, no crack, or any damage. There is no cold weather testing required in the ULC-S636 standard.
  • UV Testing: ULC-S636 has no testing to cover exposure to the elements. UL-1738 must pass its physical properties tests after light and water conditioning which simulate UV rays from sunlight and rain water.
  • High Temperature Testing: UL-1738 requires that vent system is tested 70⁰F (38.8⁰C) higher than the rated temperature. This is not required for ULC-S636.
Given the more stringent requirements of the UL-1738 standard and the additional tests required to assure its materials can survive the real world environmental stress, it is apparent that the UL-1738 standard should continue to be the standard strived for by vent manufacturers and required by code officials.

Is Centrotherm the only manufacturer with products listed to UL-1738?

No. There are multiple manufacturers and material types listed to UL-1738. Below is a partial list of approved manufacturers and materials. There are currently additional manufacturers in testing.