Code / Listing FAQ

Why did Centrotherm seek and obtain a UL-1738 product listing?

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. The UL-1738 safety standard incorporates 70⁰F of safety margin above the listed maximum operating temperature. This means that InnoFlue® is listed at 230⁰F maximum flue gas temperature, but was tested by Intertek at 300⁰F. This ensures that that the vent system can safely operate even if there is a significant increase in the appliances flue gas temperature.  In 2017, NFPA added language to the national fuel gas code in support of utilizing UL-1738 listed flue gas vent systems for category II and IV appliances. InnoFlue® is tested by Intertek and listed to UL-1738.

How long has InnoFlue® Polypropylene Flue Gas Vent Systems been on the market?

InnoFlue® has been sold in the United States and Canada since 2009. Polypropylene flue gas venting products have been sold throughout Europe for over 25 years. This technology has been proven to be safe and reliable. It is the dominating technology in Europe and is utilized by all European original heating equipment manufacturers.


Is PVC used as a Flue Gas Vent System in Europe?

No. PVC is not used as a flue gas vent system in Europe due to PVC’s lower maximum operating temperature, environmental health, and safety concerns.

Why is polypropylene the correct flue gas vent material?

Polypropylene flue gas vent systems are specifically engineered for the application. Polypropylene has a vicat softening temperature (the temperature at which the thermal plastic deforms under load) that exceeds 300⁰F. This allows the safe use of InnoFlue® Polypropylene Vent Systems to sustained temperatures up to 230⁰F, after subtracting the 70⁰F of safety margin. Condensing heating appliances (furnaces, boilers, tanked water heaters and tankless water heaters) are typically designed to have flue gas temperatures below 150⁰F when operating at optimum efficiency. System design (inclusion of base board in hydronic systems or use of multiple zones in furnace systems), building owner comfort (higher reset temperatures), required 180⁰F hot water or a lack of routine field service (operating with scaling on the heat exchanger or clogged filters) can cause heating systems to generate flue gases in excess of 200⁰F.  Schedule 40 PVC “is intended for non-pressure applications where the operating temperature will not exceed 140⁰F.”* At 140⁰F, PVC has only 22% of its original design strength remaining.
*Per the Charlotte Pipe Schedule 40 PVC Submittal Document.


Is InnoFlue® approved by the Massachusetts Plumbing Board?

Yes. Centrotherm’s InnoFlue® is approved by the Massachusetts Plumbing Board for its intended use as a flue gas vent system.


Is polypropylene available from multiple manufacturers?

Yes. Polypropylene flue gas vent systems are available from at least 4 U.S. manufacturers.

Where does the supply of polypropylene flue gas vent systems originate?

Centrotherm’s InnoFlue® product line is proudly made in the USA. Our product is manufactured in our Albany, NY facility. Competitors’ polypropylene products are also manufactured or supplied out of the North East.

Where can I buy polypropylene flue gas vent systems?

Polypropylene is readily available at numerous plumbing and HVAC suppliers throughout Massachusetts. Currently over 15 different wholesalers stock polypropylene at over 100 locations within the state. Competitor’s polypropylene flue gas vent systems are also available online through outlets such as Home Depot.

Does the use of polypropylene increase the overall cost of an installation?

There is a slight material premium for polypropylene. However, installers can expect labor savings of up to 70% due to quicker installation times.

Is the market sufficiently familiar with polypropylene to switch?

Yes. Industry organizations such as AHRI and HARDI have been involved in discussions on safe and proper flue gas venting over the last 8 years at NFPA, UL, State, and local code meetings. Over the past 8 years, all major heating appliance manufacturers now have polypropylene listed as an approved flue gas vent material in their installation & operations manuals. Individual municipalities, large cities such as New York, and other states/provinces such as New Hampshire and British Columbia have already taken action by eliminating or restricting the use of PVC as a vent system.