Failures on PVC ??

Are you having problems yet with PVC ???

I heard by a little birdy that people on the east coast are starting to have failures on condensing boilers using PVC pipe. Is this true ?? I seen now manufactuers are starting to put exhaust temp sensors to protect the PVC pipe. My question is can we really have expansion / contraction problems with PVC pipe ?? Why are the europes not using PVC ??

I've had a gut feeling about this subject..................

In my observations of systems I run across in my travels through peoples basement's, I see lot's of condensing equipment that is not running in condensing mode. This goes for both boilers and furnaces. Condensing boilers are being installed in high temp applications and wired to run to high limit and shut off. Furnaces are installed with little regard to air flow causing constant bouncing off the safety high limit. In addition there are some condensing appliances in which only a portion of the HX actually operates in condensing mode. The other half isn't much different than a normal HX.

This simply has to place the flue gas temperature outside the anticipated range of operation. My guess is that PVC is OK to use when all things are perfect but not so when conditions get outside the lines. Being outside the anticipated range of operatoin is something that happens all to regularly due to installations done by people who don't know and/or don't care. I'll take a manufacturer supplied venting system or stainless steel any day of the week instead of PVC DWV pipe.

PVC

The vent system must be tested and specifically approved for the use with the approved appliance. If the vent system is not a tested and labeled component of the appliance, the material must be approved for use with the appliance and installed in accordance with the manufacturer's installation instructions.
Jeff, below hinted that "foam core" PVC wasn't approved. I too have concerns about foam core (cellular), however some manufacturer's are allowing the installation of it with the codes support. Foam core can be used, but only when the specific ASTM number is advised and the ASTM number is written on it.
Gas burning appliances (listed as category II, III or IV) require special vent systems that are specific to the type of appliance. Special vent systems are typically associated with mid- to high-efficiency appliances and include vent materials such as polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC) and special alloys of stainless steel.
A primary consideration for the design of a special vent system that serves a high efficiency appliance is the selection of the material that is capable of withstanding the corrosive effects of condensate. Flue gas condensate is slightly acidic and corrosive and can deteriorate many vent materials. Sulfer in the fuel and halogens carried in the combustion air can combine with the combustion products to create acids. To prevent the corrosion of a vent and possible escape of flue gas, metallic flue passageways can be protected with appropriate coatings; however, any imperfections, pinholes or discontinuites in the coating can create areas for condensate to collect and accelerate the deterioration of the chimney of vent. The solution to this problem has been to use a material such as PVC, CPVC or high-temperature plastic that is resistant to acidic condensation and compatible with the temperature of the appliance flue gases. Plastic pipe is a suitable material because it is impervious to corrosive condensation and can easily be designed to drain off accumulated condensate. The flue gas temperatures of most condensing-type appliances are not high enough to effect such materials adversely.
Special vent systems must be designed and installed in compliance with the manufacturer's instuctions, which will specify installation requirements that are specific to that type of vent and appliance. For example, a maximum developed lenght, a maximum number of directional fittings, fitting turn radius and specific support requirements will be specified for special vents using plastic pipe. Special vent systems also have special vent termination requirements, and typically incorporate condensate collection and drainage fittings and connections.
As far as the "little birdie" is concerned. I believe it probably roosted under one of my vent terminations (nice N' moist and warm), probably caught a cold or the bird flu perhaps, and failed to inform me of these failures.
Where did you get this information?


Robert O'Connor/NJ (east coast)

I agree with S Ebels

And because of the facts mentioned above I will ONLY ever even consider using a PVC exhaust system if it can all be ripped out and replaced easily. I have had to be the second man in on too many jobs where the original guy ran PVC through the house and it had to be ripped out 10 years later. I so far I have been fortunately able to avoid using boilers that use PVC. However I will not mind using one like the Munchin, etc as long as the boiler sits next to an outside wall, making for a very short venting run, and if need be down the road the whole venting system can easily be replaced. Even then I would rather use a company that uses a proprietary venting system that it sells with the boiler like the Vitodens.

It's funny how some of us who do a lot of service work (re: do not run from a problem job) spend extra time and money on new installations to install them by the book... or better!


Cosmo Valavanis

Robert

I wasn't tryin to cause problems. I was just wondering if what I heard was true or not. I was told by a manufacters rep this info. I wasn't holding him to his words but only to hear what the east coast family has to say. What I read on the wall helps me out daily, and sometimes I can't always put in my .02 cents though I wish I had the knowledge to, in due time though. All the wallies I see frequently on here I dearly respect what you all have to say. Without some off the topics that come up here, how would we all fix the problems that come up across the U.S. in our industry ? This thread was started only put to bed what I heard, not to scare people away from using PVC / CPVC pipe. I have lots of boilers in use with PVC, and not a lick of problems with the systems vents and sounds like I shouldn't either.



Shaun

This is all interesting but ..

Cosmo claims ( if I read him right ) to have replaced PVC venting for failure. Is this true Cosmo ?

How did the PVC fail ?

We have installed some boilers with PVC and we see Many Others installed with PVC vents and I have yet to here of failure in the field.

Yes I remember the Plexi-vent fiasco but I have yet to come across OVC venting that has failed. Anyone have real life problmes with it ??

Scott

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\"Then 3 other guys come in say \"

I have unfortunately found that 95% of customers will look for, and take, ANY excuse to spend less money. Who cares how well it works, all systems just blow hot air anyhow, don't they?

Joel/Steve

That's just it, people don't look at the entire picture. They have no clue that increasing the return air (if it's undersized) can actually improve efficiency.

Many years ago, I went to a house that need some work to be done. It was built as a weekend cabin on a lake when the current owner bought it. The owner bought a furnace and had the maintenance man (Light bulb changer) install it. The furnace had 8 inch round pipe for the return for the 75K furnace and it was vented outside the house through a foundation vent with an elbow and a rain cap right against the siding! The owner/seller wanted it fixed (only to the degree that the buyers inspector said so the house could be sold, nothing else. I did that, but added on my invoice the other problems I saw. The seller wasn't happy. I never heard from the buyer....

compared to the stainless you mention above how does 316 L compare

Anecdotal evidence

Given that we install forced hot air systems and we've always been drawn to cutting-edge technology, we latched onto condensing high-eff furnaces from their first appearance. Lots of PVC vents out there that have yet to show any signs of a problem. We avoided the plex-vent installs for some reason, so they aren't an issue for us. However, we're one of the few firms that will tackle plex-vent replacements under the recall when contacted.

However, we did have one 80+ furnace installed on PVC because our supplier said that was OK. Two years later, we discovered the first few feet were discolored (tinted yellow if I remember correctly) and we decided to install a Tjerland kit in place of the PVC. Still working like a champ.

Furnaces and condensing boilers on PVC the same? No way. Furnaces almost always "see" the same return temp of about 68 F (under most conditions). Boilers, on the other hand, might "see" anything from that 68 F on a cold start to 200 F in a system where the installer cut off the corners in order to cut install costs by reducing the amount/size of the heat emitters.

High eff condensing boilers do very well with lower outlet and return temps and I've found the exhaust temp trails the outlet temp by about 20 F. The long & short of it, is we are exceeding the PVC manufacturers temp rating for their product. One mfg stated (to me) that this remains OK because the exhaust gases are "wet" and that the condensation "cools" the PVC sufficiently. My own observations would confirm that the walls of the PVC are most assuredly wetted, but that condensation must be at, or close to, the exhaust gas temps (my opinion only & not based on any actual temp readings for the condensate droplets). Sticking to their line of reasonong, the exhaust gases are in motion and, therefore, generating an evaporative wind-chill effect on the wetted walls of the tubing.

Ever since the first shot across the PVC bow (that I heard), I've been taking a closer look at all PVC exhaust vents. As for leaking joints? The only ones that can leak would have to be from stress fractures through the fitting, fitting AND pipe, or poorly made joints where the installer failed to swab the pipe and joint with sufficient solvent-cement, joints assembled without primer or use of the wrong solvent-cement. Properly made PVC joints become "welded" and bond the pipe to the fitting.

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