You Have Choices for Your Boiler Flue Materials

United Energy Products prides itself in being your local go-to expert when it comes to venting your fuel burning appliances.  We’ve invested time and talent over the years convincing you to avoid PVC for venting your high-efficient, condensing boilers, particularly for boilers in excess of 1,000 MBH.  Many times we have jokingly said, “there aren’t a lot of opportunities to kill people in your HVAC designs and installations, but this is one of them.”  Seriously though, we’re delighted that many design professionals and contractors appreciate the value and benefit of stainless steel, Category IV, venting for condensing boilers.

It’s time to take this conversation to the next level.  Now that we’ve made the case for stainless steel over plastics, which type or grade of stainless steel is the best choice?  The combination of metals that go into the alloy are different for each grade, giving them unique properties and benefits.

AL29-4C was first developed by Allegheny Ludlum (hence the AL in the alloy name) in the early 1980s for the power generation industry for condenser tubing.  Later they marketed for vent pipe for Category II, III, and IV gas-burning appliances. When it comes to Cat IV condensing appliances people have equated the terms stainless steel and AL29-4C as if they are the same thing.  AL29-4C is a type of stainless steel, like 304 or 316 or 430.  Allegheny Ludlum has done an excellent job of marketing it as the only choice.  Don’t misunderstand us, AL29-4C is an excellent choice for venting due to its resisting to pitting and corrosion.  So is 316L!  Manufacturer’s that comply with UL1738 are required to meet minimum requirements for corrosion resistance.

There are differences in metals content the alloys.  AL29-4C contains Titanium, while 316L contains Molybdenum; both of those metals increase the corrosion resistance of the alloys.  You could make the argument that AL29-4C is “better”, but the important thing to recognize is that AL29-4C is a proprietary alloy and will always be more expensive.  Maybe you don’t care.  Maybe you prefer Coke and you want Coke every time and you don’t care how much Pepsi cost.  But if you’re one of those engineers or installers who wants a soda and the Coke costs 25% more, you might be thinking Pepsi isn’t so bad after all.

In our research for this article, we endeavored to find articles that compare the grades of stainless steel in the application of Category IV venting.  There aren’t many.  There’s a really good one on the Allegheny Ludlum website… you can imagine what they have to say about 316L!

In our years of assisting with the design, purchase and installation of flue systems here at UEP, we can confidently state that the problems we’ve encountered with Category IV venting have more to do with the improper sizing and installation than with the grade of stainless steel.  We’ve seen many successful applications of 316L stainless steel for boiler flues.  It’s also fair to say that we’ve seen may successful applications of AL29-4C stainless steel for boiler flues.  The choice is yours; we happily offer both products!

We believe that knowledge is power, and that having a better understanding of your choices for materials selection will aid in the specification for your particular application.  Specifying systems that comply with UL1738 is imperative regardless of the material selection.  For assistance with the application, design, purchase or install of your next boiler flue project, please contact us.

United Energy Products prides itself in being your local go-to expert when it comes to venting your fuel burning appliances.

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