Why is AL29-4C so heavily embraced by the venting industry when it comes to material grade stainless steel? Why does 316L seem to be the second choice, when in fact it meets the same UL
standards and deserves equal consideration? In the mid to late 1990s, the venting industry developed High Temperature Plastic (HTP) venting systems listed to UL1738 & ULC-S636 that could withstand temperatures up to the 400F range. Furnace and boiler manufacturers embraced the idea and approved these venting systems for their new fan assist furnaces because of flexibility surrounding the installation. However, after a few years of use, problems began
occurring in the system. Silicone (used for securing and sealing joints) started failing and joints were losing seal, causing condensation or complete joint separation resulting in large point-of-connection leaks. Eventually, research conducted by Battelle Labs, among others, revealed that the first-generation resin being used was overly susceptible to environmental stress, cracking, and aging. The research identified a second-generation resin as a way to compensate. However, that silicone sealant didn’t hold up well when in contact with acidic condensate. Battelle was then able to identify AL29-4C as a candidate for metallic system material that could withstand the effects of these highly acidic condensates. Boiler OEMs who had more severe issues with higher vent pressures and corrosive condensate embraced the AL29-4C system which became the impetus for the industry moving toward the special gas vent market. What seems to be a little-known fact is that 316L is
actually an equal substitute for AL29-4C as it is listed to the same standards and holds up just as well in corrosive environments. 316L can also be sourced from multiple suppliers while AL29-4C has only one. In terms of price, 316L is less expensive per pound, which provides the customer upfront savings. It is easy to understand why the industry has so heavily embraced Al29-4C, however, 316L is a great option as well and holds its own when it comes to the special gas venting market.
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