Document Addresses Connecting Plastic Pipe to Tankless Water Heaters

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The Plastics Pipe Institute, Inc. (PPI), has published a new recommendation related to the direct connection of plastic piping materials CPVC, PE-RT, PEX, and PP to tankless water heaters.

Available on PPI’s website, PPI Recommendation H Direct Connection of Plastic Piping Materials to Tankless Water Heaters for Domestic (i.e. residential) Applications provides clear guidance on the question of direct connection of these piping materials to tankless water heaters. PPI is the major trade association representing the plastic pipe industry.

“PPI Recommendation H answers questions which plumbers and builders have been asking about whether it is appropriate for plastic pressure pipe materials to connect directly to the cold-water inlet and hot-water outlet of domestic tankless water heaters, without the use of metallic flex connectors. Based on our research, these direct connections are usually acceptable,” explained Lance MacNevin, P. Eng., director of engineering for PPI’s Building & Construction Division.

“To help answer this question, PPI and our members researched Canadian and US model plumbing codes,” he continued, “reviewed the published literature on dozens of tankless water heaters, and confirmed the recommendations of plastic piping system manufacturers. Based on the proven high-temperature capabilities of these piping materials and the relatively consistent water temperature control of modern tankless water heaters, there is no technical reason to prohibit direct connections. Of course, installers must follow local code requirements and the manufacturer installation instructions.”

“As stated in Recommendation H: Piping systems using the materials CPVC, PE-RT, PEX, and PP, which carry a pressure rating of 100 psi at 180°F (690 kPa @ 82°C), and which are intended and certified for hot and cold potable water distribution systems according to industry standards and relevant codes, may be connected directly to tankless water heaters which are intended for domestic (i.e. residential) applications, unless prohibited by local plumbing code or the specific water heater manufacturer.”

According to PPI President David Fink, “The research on this topic was prompted by an inquiry from a major builders group. The rapid development of Recommendation H demonstrates the ability of PPI members to collaborate and respond quickly to industry questions about responsible usage of plastic piping materials.”

Published on PPI’s website directly at recommendation-h-direct-connection-tankless, Recommendation H is one of several PPI documents related to the design and installation of pressure pipe materials for plumbing and mechanical applications, which are all published as a service to the industry. Additional information about PPI’s Building & Construction Division can be found at

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