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When condensing appliances first came to North America, it was a bit of a “cart before the horse” scenario when it came to the venting material options available. The industry has since overcome that issue.
Condensing appliances generate lower stack temperatures than their standard-efficiency counterparts but also produce caustic flue gas condensate. As a result, traditional metal venting material can’t be used on high-efficiency gas-fired appliances. In the early 2000s, AL29-4C, polyvinyl chloride and chlorinated polyvinyl chloride were the only venting options.
In most jurisdictions, PVC isn’t approved for condensing appliance venting, at least not when connected directly to the appliance. CPVC is suggested by most manufacturers for the first 30 or so inches, at which point the vent can usually transition to PVC. This is because it’s possible to see flu temperatures as high as 180 degrees at some point during a cycle. This occurs most often at the beginning of a cycle before the unit starts to condense or in the event, a heat exchanger is neglected and becomes so dirty that the transfer of heat is impeded.
Chemically speaking, CPVC is different from PVC in that it has a higher chloride content, meaning it can withstand higher temperatures. CPVC is approved for 190 degrees and PVC is approved for 140 degrees. Local codes vary, as do manufacturer guidelines, so don’t take my word as gospel.
Horse catching the cart
We started using polypropylene venting products about eight years ago. It’s been available in the United States for about 15 years, but it’s been used in Europe since the early 1990s.
Polypropylene is a polymer that’s tough, resistant to harsh chemicals and can withstand high operating temperatures. It’s approved for temperatures up to 230 degrees. Regarding use in the boiler room, the cost of PP venting typically falls between CPVC and PVC.
There are several manufacturers of poly vent systems in the United States today, with Centrotherm and DuraVent being the biggest names in the game. Both companies offer a wide variety of pipe sizes, fittings, terminations, flexible pipe and cascade kits. The options are nearly endless; plenty of upside.
Whenever possible, we like to buy everything we install from a single rep. I’m big on relationships, and so is Dave Raabe at ROI Marketing. When it picked up the Centrotherm poly line, we began installing it. We use it on all the condensing appliances we install, except for several pool heater models not approved for poly venting.
One of the biggest advantages of this product line is the clip system that holds the pipe and fittings together. The ability to disassemble and reassemble the pipe allows technicians to remove the venting for better service access. If the flu is clogged, it will enable them to open it up to look for an obstruction.
Thanks to the clip connection system, our technicians are no longer exposed to the noxious fumes created by PVC glue and primer, and the pipe never has primer stains on it, which is a pet peeve of mine. Poly pipe is gray instead of white, so it doesn’t show dirt after bouncing around in the back of a van.
It’s also much lighter than PVC or CPV, which is a major advantage on big commercial projects where giant flu pipe is often installed overhead. We’ve also found that the availability of PP is much better than CPVC.
PVC and CPVC aren’t UV-protected, which means they can, over time, degrade when exposed to sunlight. This is generally only a concern on vent terminations. I don’t know about other brands, but Centrotherm offers a UV-protected product, which is black in color.
We transition from its standard poly pipe to UV-protected pipe before a wall or roof penetration. This protects the venting system from UV damage and ensures that the visible part of the system is black. It looks nicer than gray and much better than white.
PP flu pipe cuts more easily than CPVC or PVC because it has a thinner wall. We’ll use a reciprocating or chop saw on large pipe, but a tubing cutter can be used on smaller-diameter pipe. After cutting poly pipe, it’s important to bevel the edge of the cut to ensure that no damage is caused to the fitting gasket upon assembly. This, along with the application of lubricant, takes a few additional seconds.
We’ve only found one challenge — though a minor one — with PP venting. Due to its thinner wall, it’s more likely to sag than PVC or CPVC. We add more support to the pipe across horizontal runs to address this.
By switching to PP venting, I know my technicians are using a lighter, easier-to-install material, my customers have received the best venting product the market has to offer, and service work can be conducted rapidly if there’s ever a reason to disassemble the flu.
As always, be sure your venting system meets local codes and is approved by the manufacturer of the appliance you’re installing.