Is PVC an acceptable vent material for flue gases?

Steamhead

Well, I'm sure

that feature was one reason you chose the Munchkin ;-)



On the units described in this thread where the PVC overheated- did any of them have this type of dial-back setup, or something else that would prevent overheating? I'd be willing to bet they didn't.



It seems to me that the venting of traditional non-condensing equipment was designed with a certain safety margin (or evolved to that point) so it would hold up under extreme trouble conditions (for example, one of my Dead Men's Books describes improper coal-to-oil conversions where the stack was red hot). PVC venting of condensing equipment apparently does not allow this margin of safety.



Unless and until there is a clear standard, maybe we should steer clear of PVC for venting.



I'm heading out to a job- back later.

Tim McElwain

pipe4zen it was not my intention

to open this forum for advertisement of anything. The issue here is safety both short term and long term. Mr George and I have no personal relationship of any kind. I invited him here to defend his findings on the PVC pipe issue. Healthy discussion and allowing all opinions to come forth is what solves problems if in fact there is a problem.



I take some issue with the problem versus the patents pending and personally feel it is somewhat a conflict of interest. Mr George I am sure can defend himself on that issue. I have received several private e-mails voicing concern over his perhaps going forward and making money from something he is dealing with as a code person.



Then there is a fact over and above the safety issue which is directly related and that is liability. After many years in this industry (over 55 years) I have found in court cases (I am a registered expert witness) that often the courts rule against the contractor who may have knowingly done something or used something which was questionable or in fact had no approval from a governing body. I am always first and foremost looking to help and protect my fellow technicians. I worked as a serviceman and educator in the industry for many years and am now strictly an educator. I am trying to help everyone to come to some conclusion on this subject. I interjected the discussion on polypropylene to perhaps find an approved solution.



As for the several e-mails I have received accusing me of getting paid by some manufacturer or agency that is not true. My income is derived from my consulting and educating practice and I am not directly affiliated with any company. I do offer my consulting services to some control companies and have done consulting for a number of them. That does not however put me in any ones hip pocket.

Plumdog_2

flue gas temp sensors

Trinity, Lochinvar Knight, Munchkin, and Prestige all are equipped with flue gas temp sensors. Pretty sure the Polaris water heater and the Lennox Complete Heat are so equipped as well. How many of the others are so equipped? I can't recall seeing them on scorched air equipment; but that doesn't mean they aren't there. I've seen supply air temps over 150 degrees, meaning the vent temps oughta be that high as well. Does anybody know how many 90% furnaces are out there? Better to have an airtight vent than a leaky metal vent. Hardly anyone seals the gores on the vent ells like your supposed to, and they leak CO all day long.

Jean-David Beyer

Flue Gas Sensor.

My W-M Ultra 3 has a flue gas sensor, but the U-control (the controller for the boiler) will not fault until the flue gas gets up to 210F, so it will hardly protect 140F PVC.



The default setting for their Indirect Fired hot water heater is 190F. I run mine at 175F. The domestic hot water is set to about 120F. The supply from the boiler can often get to 175F just before the domestic is satisfied. The return water is usually around 20F less, so say 155F. I suppose the heat exchanger is not 100% efficient, so the flue gas almost certainly exceeds 155F as it leaves the bottom of the heat exchanger. It travels through about 2 feet of uninsulated stainless pipe to the top of the boiler, where it transitions to 3 inch PVC. It might be slightly less than 155F at the top, but I would not want to make a bet on that. The outside temperature of the vent pipe I measured a while back, but I do not remember what it got to. Lots less than 140F, but it is probably the inside temparature that matters.

CMadatMe

Beating A Dead Horse

I think the horse has been mutilated to this point. Everyone is going to have their own opinion on this matter and rightfully so. In the end I just look at one thing.



Trial and error is not in the best interest of public saftey. Just because it works itsn't the right way to do or justify a means. Why the heck do a heat loss. The system will work right. We all preach to those that come here to do the right thing and I would hope we would all want to see the testing data equipment mfg's have that allows PVC venting. If the testing data shows it is a safe means then so be it. Call the mfg of the equipment you use and ask for it. If its safe then what is there to hide.



The lack of mfg's to respond on this issue within itself fuels the issue. Can we all agree on that. Why not use our voice as a whole to ask the questions and begin a new thread with what we find out. I'll start the thread with Viessmann's stance since they to my knowledge are the only mfg that has a printed statement concerning this issue. Everyone else can add from there what they have found out from the mfg of the equipment they use. It can be a no comment anwser if need be.



In the end we are all professionals that do their best to do the right thing by code and the pride we carry in what we do. Until I see a stamp on PVC that says I'm using a safe vent material to remove combustion gases that's the day I will start using and recommending it. Until then, I'll stay away from it.

HDE

"Until then, I'll stay away from it."

Thats an interesting statement since many products you carry as a distributor vent with PVC.

How will the owners and bosses that employ you feel about that?

CMadatMe

Interesting

I get up each morning as they do, put my pants on the same way they do, get my coffee like they do and give my best each day like they do. Do you honestly think I would give in my belief concerning this issue because someone told me to? That would never happen. There would also be a conflict of interest for me since when I do my Viessmann Trainings and we get to the vent topic I'm already swimming in that water. How can I preach one thing and then another? That's being an oxymoron.. By the way I only have two bosses, my 3-1/2 yr old son who is my world and my wife who is in Myrtle Beach visting her father..

Ron George

Is 148 degree pipe listed to a standard not recognised by the code acceptable?

Remember, most PVC pipe manufacturers in their literature do not reccomend PVC piping be utilized at temperatures above 140 F.  If you use the IPEX product, they allow 148 F for their product and with a temperature limitation of 148 F.  I must remind you, most boilers, water heaters and furnaces will have flue gas temperatures well in excess of 148 F.  Using the PVC in a system that exceeds those temperatures would be a violation of the pipe manufacturers product limitations. (even if it is the 148 F pipe)   Then the contractor takes on all the liability.  Most PVC pipe manufacturers have reviewed this and decided to stay away from endorsing PVC for venting combustible flue gasses because there is too much liability.  A few have offered it and I feel that is a gamble. It is just not safe. You can chosse to install PVC that is listed to ULC S636 and take a gamble that a mechanical inspector in the U.S. will accept that standard.  If you are ein Canada and you are sure the system is designed to operate with flue gas temps below 148 you are OK.  But, the standard is not listed in the codes in the U.S. and therefore not an approved standard in the U.S.  Canada has been allowing it, but there has been some controversy there too.  Good luck if you choose to gamble and install PVC.  Stainlees steel systems are available and if you join them properly (in accordance with the manufacturers installation instructions and seal the joints) it does not leak.   

Ron George

Only one pipe is discolored

The only PVC pipes in the above photo are uninsulated and connecting to the top of the appliance.  It appears JDB was comparing the color of the water pipe insulation jacket color to the color of the PVC pipes.  The insulation jacket on the adjacent water piping is bright white compared to an off white for the PVC.  There does not appear to be any discoloration of the combustion air inlet PVC pipe to me.  But there is a definate difference in color between the inlet PVC pipe and the outlet PVC pipe.  The heat from the combustion gasses is definately affecting the flue gas exhaust pipe different than the combustion air inlet pipe.  As for the photo below it shows a similar situation. If the discoloration was from car fumes as suggested below, I would think both pipes would be discolored the same.

HDE

Ha

I doubt Jim, Pete, Bill, Melissa, Justin & Rick feel that way. They desire sales, discriminate product due to your product venting principles and PVC could be your own personal demise, am I right?

Sorry about the wife being your boss, when did you lose that one?

CMadatMe

Don't Discriminate Product

I never said I discriminated equipment just the practice of venting PVC when there are other means. Like I said, in my Viessmann classes the hot topic is always the venting issue. If I flip flop like a politician would I not loose my credibility?  Throwing names has no effect to my stance. Next time you come to Hawthorne stop by and say hi.

HDE

I will

i haven't seen Rick or Jim in sometime. There was awhile there it seems I ran into them every 3 months or so.

Ron George

Reply to Icesailor

Ice man, Many PVC pipe manufacturers do not reccomend usng PVC for venting combustion gasses.  They list the limitations of their products in the technical manuals.  If someone chooses to use their product for something other than its intended purpose, they cannot be held responsible for a boiler or furnace manufacturer claiming you can use PVC pipe to vent combustion gasses.  Manufacturer's also do not have control over many of the other "redneck engineering" uses uses of PVC pipe. (furniture, structural supports, handrails, flag poles, fence posts, potatoe cannons, compressed air pipes, rocket launchers, air cannons, combustion gas flues, etc.)  There are no industry standards in the U.S. approving of most of these uses.

Ron George

Website with lots of ides for use of PVC pipe

http://www.pvcworkshop.com/SubmittedProjects.htm 

Not all of the ideas in the aboe website are safe. Some are comical and some are practical, but most are not approved uses for the product. This just shows the wacky ways PVC pipe gets used.  Duct tape probably falls into this same category. I call it "Redneck Engineering".  Many manufacturers have jumped on this bandwagon and in my opinion, they are taking a big risk if there is ever a problem and they are recomending PVC pipe for venting combustion gasses in their literature.

Tim McElwain

This from Charolotte Pipe and Foundry Company

Should Plastic Pipe & Fittings Be Used to Vent Combustion Gasses?







Use of plastic pipe to vent combustion gasses produced by water and space heating equipment has become common practice among plumbers and builders. Some equipment manufacturers expressly recommend this practice. Occasionally, Charlotte Pipe is asked for its position on the use of plastic pipe and fitting products for this application.

Industry Standards

A variety of organizations produce standards for the construction industry. The best known of these organizations is the American Society for Testing and Materials International (ASTM). ASTM standards are developed by committees of industry experts and approved by the ASTM organization through a rigorous consensus process. These standards specify dimensional, performance and test requirements for various materials, including piping products. Manufacturers like Charlotte Pipe produce products that conform to these published standards. None of these standards addresses the use of plastic piping to vent combustion gases.

Equipment Manufacturers

Manufacturers produce a wide variety of gas-fired water and space heating equipment. These manufacturers may specify plastic piping for venting of combustion gases, citing these ASTM and other standards within their technical literature:







ASTM D 2241    Specification for PVC Pressure Rated Pipe

 

 

ASTM D 1785  Specification for PVC Plastic Pipe, Schedules 40, 80 and 120.

 

 

 

ASTM F 891  Specification for Coextruded PVC Plastic Pipe With a Cellular Core.

 

 

 

ASTM F 441  Specification for CPVC Plastic Pipe, Schedules 40 and 80.

 

 

ASTM D 2661  Specification for ABS Schedule 40 Plastic Drain, Waste and Vent Pipe and Fittings.

 

 

ASTM D 2665  Specification for PVC Plastic Drain, Waste and Vent Pipe and Fittings.

 

 

 

ASTM F 438  Specification for Socket Type CPVC Plastic Fittings, Schedule 40.

 

 

 

ASTM D 3311  Specification for Drain, Waste and Vent Fitting Patterns.

 

 

ASTM F 628  Specification for ABS Schedule 40 Plastic Drain, Waste and Vent Pipe with a Cellular Core.



 



Although these standards specify dimensional, performance and test requirements for plumbing and fluid handling applications, and are often used to refer to or describe a particular type of pipe, they do not address venting of combustion gasses. References to these standards by water heater or space

heating equipment manufacturers should not be viewed as acceptance or approval by the ASTM for these applications.

Conclusion

At present there is little data available on the safety or durability of plastic pipe products used to vent combustion gases. The ASTM has not addressed this application, and the available data is insufficient for the plastic pipe and fitting industry to develop consensus specifications or guidelines. Equipment manufacturers are most knowledgeable about their own products and are best­ equipped to determine how their gas-fired heating equipment should be vented. Accordingly, Charlotte Pipe recommends that inquiries about the suitability of plastic piping systems to vent combustion gasses be directed to the manufacturer of the water or space heating equipment being installed.

 

Tim McElwain

Here is some more

input from a boiler manufacturers rep.



Hi Tim,

 

I felt a need to contact you regarding something that was lacking from all of the replies on PVC pipe..



 

We call for the installer to use the CPVC venting material (30") that we provide to allow for cooling of the flue gasses to the tolerance that the PVC resin manufacturers call for or 140F. We also state that the PVC pipe being used be "SOLID CORE" Schedule 40 and NOT PVC "Cellular or Foam Core" pipe. Several years ago I was in my driveway outfitting one of our rolling display vans with two Alpine boilers that were stacked to demonstrate that capability. I decided to use PVC on one of them and Polypropylene on the other to show the different vent materials. When it came time to pick up some Schedule 40 PVC pipe from a local distributor, I was disturbed to find that very few RI distributors even carry "solid core" pipe anymore. All I contacted only had "Foam Core" in stock. To be politically correct in continuing my search for "Solid Core" pipe I ended up at The Home Depot.



 

As Mr. George stated, many contractors prefer to use inexpensive items in an effort to stay competitive for fear of losing a job. The thing that troubles me is that I have been on numerous jobs where "Cellular Core" was used, either due to ignorance to the difference or due to trying to stay competitive. I had many installers remove the pipe and replace it with the correct pipe. We also call for CPVC pipe to be used when the piping is enclosed in a vertical or horizontal chase way as the pipe temperatures can elevate or stack in temperature without the surrounding air to effectively cool it. Mr. George is correct regarding the stance of the Pipe Manufacturers as clarified by the attached memo from Charlotte when we were giving consideration of PVC as a venting material for the Alpine and Freedom boilers.



 

As for the jobsites that Mr.George was referencing in his article, he fails to give mention as to what grade of PVC pipe was used in the installations. I would probably think that at least some of them may have been "Foam Core" or even some other grade of PVC such as SDR pipe. I have seen PVC discolor on some jobsites where the pipe is tucked up inside of floor joists or in chase ways where traditional cooling by surrounding air is not present. Most equipment manufacturers use flue gas sensors to aid in protecting the vent system and U.S. Boiler is no different. Our control is set to kick in a Fan Rate Limiter when the flue gas temperature exceeds 192F and will activate a "Hard Lockout" if the temperature exceeds 204F.

 

 

While I have seldom seen flue gas temperatures ever reach this point, I was on an Alpine installation where the contractor installed an Alpine to only generate DHW for a motel. The boiler operated fine last year but when he turned it on several weeks ago for the summer season, it kept locking out on the Flue Gas Sensor 204F limit even though the boiler temperature was only at 150F and struggling to rise. Combustion was correct, vent installation was correct, gas was correct and the heat exchanger was spotless. Upon asking the installer what changed between last year and this year he said nothing. That's when I asked what he does with the boiler and indirects during the winter. Answer was "I blew them all out with compressed air".



 

Knowing that the Giananni heat exchanger headers are on top and the coils are suspended below, I made it clear to him that there is absolutely NO WAY that you can get all of the water out of that heat exchanger and that the water remaining in the bottom half of the coils had probably frozen and swelled the tubing. To prove this point I tried putting a credit card between the coils on the bottom of the heat exchanger, then the sides and top. It would not fit between the bottom coils but inserted easily in the upper areas. He effectively lost over a third of his heat exchanger surface area to conduct heat from the flue gasses thus the high flue gas temperatures and sluggish heat transfer.



 

As for the incidents that do happen out there, we unfortunately have no control over how these boilers and venting are installed. Provided all guidelines and warnings are adhered to, the installation should not encounter any problems. I have been on many installations where chemicals (Pool Treatment and even Miracle Gro) have been in the area of the air intake and virtually disintegrated the swirl plate in the fan shroud. I would also be safe in saying that PVC exposed to chemicals in the surrounding air could also lead to degradation of the PVC as shown in a couple of the photos posted. I'd be interested in knowing what grade of PVC was used in the installations Mr. George was referencing.

 

 

Ron George

PVC Flue Pipe Failure - CO poisoning!

I have been made aware of two PVC pipe fittings that cracked and caused carbon monoxide poisoning in a residence in the Pacific Northwest.  I visited the site and took photos of PVC pipe that was very brown and discolored within about 6 feet of the two  water heaters and two yellowish fittings that were cracked and completely seperated.  There were no expansion issues as the pipe was not restrained in any direction.  Testing the Flue gasses revealed flue gas temperatures were much higher than the system temperature and far in excess of the temperature rating for PVC pipe.  The water heaters were piped in series and both were set at 160 F.  The water heater manufacturer's literature reccomended the use of PVC pipe, even though the International Fuel Gas Code requires all flue pipe and fittings to be listed and labels for their application.  No PVC pipe and fittings are listed and labeled for use as Flue materials.  The water heater manufacturer's literature made no mention of system design limitations or temperature limitations for the Thermostat on the heater for systems using PVC flues.  The 160 degree water circulated through the heating coils for heating, and there was an ASSE 1017 mixing valve at the heaters to send tempered water to the plumbing system.  The PVC flue pipe seperation above a drywall ceiling, allowed carbon monoxide to vent into the house over several years and caused excessive mold and water damage.  The owner/occupant was a 40 yr old professional female who worked in a high paying position for a major national magazine.  She started developing a mysterious illnesses and symptoms and after a while was not able to climb the stairs in her home so she slept downstairs on a sofa.  She went to the doctors for the various illnesses and medical conditions over a several year period but no one suspected CO.  At one point she was so weak she could no longer work and she had to move to California to live with relatives.  She She continued with medical treatments in California for the mysterious illness which has left her disabled and unable to function.  She is on disability.  She decided to sell her home and the home inspector found significant water damage.  When a contractor opened up the drywall he found two completely seperated PVC flues pumping CO and moisture into the home.  The plumbing contractor saw the broken PVC pipes and called the homeowner not knowing her condition and asked if she had experienced any Carbon Monoxide Symptoms like:

•Headache, Dizziness, Nausea, Flu-like symptoms, fatigue, Shortness of breath upon exertion, Impaired judgment, Chest pain, Confusion, Depression, Hallucinations, Agitation, Vomiting, Abdominal pain, Drowsiness, Visual changes, Fainting, Seizures, Memory and walking problems.

These were many of the symptoms she had been experiencing.  The CO levels were higher than the EPA reccomendations for one 8 hour exposre per year.  She lived in this home year round with CO levels recorded in the home higher than the EPA allowable levels.   I also found it interesting that the typical CO alarm levels are much higher than the EPA maximum exposure levels.  you are more likely to experience sysmptoms prior to the alarm going off.  Stay Tuned as the investigation continues.

Ron George

Flue Temps recorded

I recorded the flue temperatures inside a PVC Pipe a few inches from the water heater flue discharge.  I did this by drilling a small hole in the PVC pipe and inserting a temperature probe.  The internal temperature reached 175 F.  The system was set at 160 F.  The Maximum PVC temperature is listed as 140 - 149 F depending on which literature you look at.  In either case 175 is too hot for PVC. 

Paul Rohrs_14

PVC Temperature

Ron,

You "recorded the flue temperatures".  Great, 175°F temp of flue byproducts.  Understood.    What were the temperatures of the PVC wall?



Best,



Paul

Mark Eatherton

This woman is lucky to be alive...

Just guessing here because I have no experience with this particular product, but if it were drawing combustion air from within the same space as the appliances location, she'd have been dead a long time ago. The tendency for CO generation from flue products leaking into the combustion zone is compounded. Flame doesn't burn well in the presence of CO2, and the CO levels increase significantly, and people suffer the consequences.



I'm thinking that the appliance is sealed combustion, drawing the air for combustion from the outside. In other words, she was being exposed to the CO that is typically found in the flue gas stream, and if properly adjusted, that concentration should be fairly low. Still not a good idea to expose yourself to the products of combustion, but not as bad as a compounded issue.



It also sounds as though this is a great example of something that SHOULDN'T be done in the field in the first place. I suspect that this lady was also exposed to a lot of water borne bacteria that become air borne while in the shower. I just received my IAPMO disc of proposed code changes, and I HOPE that I find that they have banned the use of "Open Combination DHW/ Space Heating Systems", but am not holding my breath...



Edgar Allen Poe is rumored to have been suffering from the effects of long term low level CO exposure... I hope she recovers.





I think this thread may be setting a record for the most views as well.



ME

Ron George

PVC wall temps

The infrared gun read 182.3 F on the exterior of the black plastic housing connecting to the PVC pipe the exterior of the PVC pipe just above the water heater was 163 F. The flue gasses inside the PVC pipe were measured at 175 F.  The internal flue gas temperatures were measured a couple of feet downstream of where air inlets pulled in room air to mix with the flue gasses and downstream of the fan.  The actual flue gas temperatures were much higher until they fully mixed with the room air it appears there are areas of extremely high flue gas temperatures near the heater as evidensed by the significant discoloration and cracking and separation of the PVC flue pipe fittings.   Please show me any documentation by a boiler manufacturer or a water heater manufacturer or a Furnace manufacturer that shows where they have tested and certified PVC to be used as a flue gas material and provided a guarantee that the flue gas temperature will never exceed 140 F.   The tests and the documentation simply does not exist.  There is no way anyone can guarantee the flue gas temperatures will not exceed 140 F in an extreme situation.  (Scaled up heating surface in a boiler or water heater or when there is a dirty air filter in a furnace.)  With metal flues these conditions lead to wasted energy.  in PVC flue situations it can lead to flue failure and carbon monoxide poisoning!

Tim McElwain

Another Ron George article

in Plumbing Engineer , May 2012 it can be found also www.plumbingengineer.com

Zman

Great subject!

Tim, thanks for revisiting this one.

How do you feel about polypro?

I believe the failures reported are related to excessive temps.I also think if the boiler companies are going to spec PVC the should design the boiler to lock out if the flue temp gets to hot.

I work with a building department not to far from Aspen, They have recently required pressure tests on all concealed plastic boiler venting. I think this is a good call.

Has anyone tried putting polypro gasketed or flex under pressure?

icesailor

PVC Venting:

I recently did a service call where I had installed a Ruud PVP-50 LP water heater with 3" Sch 40 PVC pipe and venting. I installed it over 10 years ago. I noticed that the inside of the PVC was black. I put my analyzer in the exhaust to see how it was running. The numbers were OK except the stack temperature. It was over 600 degrees. The white pipe was all a dark tan color.

But it's OK.

Jason_13

PVC

600f stack temp brings two questions to mind. One how is this appliance efficient with that kind of vent temp? If it is designed to vent with PVC there is something wrong. Dirty & requires service? Mod/cons normally shut down under 250f.

Second question is it safe? Tan pipe usually is very brittle and at 600f is it safe?

Henry

Article on PVC

I read with much interest the article on PVC venting. The writer is very much uninformed on PVC Venting and the standards used for various materials. The 140F that he mentions is for PVC "PRESSURE" rating. IE, at 140F the pipe can support 75 PSI. All the temperature ratings mentioned are for temp/pressure ratings. BTW, ABS pipe only starts to deform at 217F which is superior to PVC.

He also mentions that there are no standards or test procedures for plastic pipe venting. This is false. There is a UL standard called ULC636!

Nearly all failures that we have seen, have been caused by the installer and NOT the pipe. In the other cases, the equipment failed. BTW 600F stack temperature would melt completly the PVC pipe! Cracked fittings are caused by the lack of space for the pipe to expand. At one point our company was using $100K a month of AL29-4C venting material. We have had more problem with this material than any other combined!



The manufacturers have tested all sorts of venting situations before certifying an apliance to use a particular special venting system. We in the code sector ensure that the installations are safe for the user and continuously monitor what is happening  across all of North America to keep it that way.

Steamhead

Henry, that's a Canadian standard

which does not have any force in the States.



Currently, there is no standard here, and the various PVC pipe makers specifically state their pipe is not intended for use in venting combustion products, and is not listed for this use. 



For now, the pipe manufacturers probably won't seek to have their product listed for combustion venting. Why should they? They get to sell the stuff, without incurring any liability.

Mark Eatherton

Questions...

I guarantee you that Mr George will be coming by to see the responses of The Wall. My questions are;



1. It sounds as if the actual failure was possibly stress induced due to the high coefficients of expansion common to PVC plastic? If yes, would an expansion joint have alleviated this stress and avoided pipe/fitting failure?



2. Was the appliance doing only DHW, or was it also doing space heating and DHW?



3. What is the status of your patent pending flue temperature control device?



4. Why no mention of ABS in your articles?



5. Are you aware that long term exposure to Black Mold will also produce many of the symptoms that the resident of this home has experienced?



6. If you feel that the Lignin had been cooked out of the wood due to the close proximity of the PVC to wood, what do you think the chances of pyrolysis would have been at an elevated wall surface temperature associated with highly conductive, low thermal resistance stainless steel would have been?



Lastly, as an expert witness, do you think it ethical to bring this situation before the public prior to finalization of any potential litigation being closed out? You know, there are a LOT of legal beagles who frequent this site...



ME

zacmobile

PP venting

I find it curious he makes no mention at the end of the article of the various PP venting products that are available, I can't understand why everyone doesn't switch over to this in light of all the controversy surrounding PVC. I certainly have, it's only a little more costly than PVC, waaay cheaper than CPVC and outperforms either of them without the yummy solvents.

Henry

UL

Actually, it is a North American standard! Just that nobody wants to spend the money to relabel the pipe as S636 because in the US there is no need! There is "no force" as NFPA54 does not require it. The members of NFPA 54 recognise that using the existing various plastic pipes IF installed properly pose no danger to the user. You are right about US pipe manufacturers CYA. They claim that it is not a suitable use so as not to have any liability for incorrect installations and failures. They don't have to pay for certification or relabeling!



Mark, there are no expansion joints available. The installer must take into consideration the expansion of the pipe while installing. If memory serves me right, PVC will expand 4 inches over 100 feet at 70 F rise. The lowest plastic was ABS 1 inch! I have all the expansion rates in my office. I have seen busted fittings due to expansion and incorrect installs!

I have checked my own home PVC vent after 10 years. There was a slight brown discoloration most probably due to Chloride removal. This is something I have seen in an aquatic lab when the numb-nut ING specified sch 80 PVC for a pure water aquatics lab. If the vent was cracked, it sent warm humid air on the wood creating spores and mould for who knows how long. I am sure that no preventative maintenance was done according to the certified manufacturers instructions.



As among other things, a forensic investigator for insurance companies, an expert witness in litigation and a voting member of the National Gas Code and 7 sub-committees, I find Mr George's motive to publish such an inaccurate article as having perhaps personal motives! I am sure that some legal buzzard will use his article to crucifix someone without all the expertise to defend himself! It is very shameful.

Steamhead

The lawyers are already doing that

I believe in the Lofgren case in Colorado (which is the one we've heard the most about), the pipe manufacturers were sued, but they were able to document that their PVC was not, and never was, listed for venting combustion products. So they were told they could go home. 



Things really are different south of the border, Henry. Our Codes require the stuff to be listed, same as yours, but it probably never will be until the listing requirement is strictly enforced.

Ron George

PVC Failure Article

PVC flue pipe failure

By Ron George,CPD,

President, Ron George Design & Consulting Svcs.

In the May 2011 issue of this magazine, I wrote a column titled, “Is PVC an acceptable vent material for flue gases?” in which I pointed out many problems and challenges associated with venting flue gases with polyvinyl chloride (PVC) pipe. In the March 2012 issue, a representative of the Air-Conditioning, Heating and Refrigeration Institute (AHRI) wrote a letter supporting the use of PVC pipe on behalf of their appliance manufacturer members that use PVC as an alternative to the stainless steel or high temperature plastic flue venting materials that are listed for use.

AHRI is an advocate on behalf of their members; they lobby at all levels of government, including at model code hearings. AHRI’s government affairs staff works closely with congressional staff on legislation that impacts the industry. In this case, it appears that they were lobbying the readers of Plumbing Engineer on behalf of the manufacturers of fuel burning appliances such as water heaters, boilers and furnaces that are recommending use of PVC pipe for venting combustible gases.

Some people have asked why I am making such a big deal over using PVC for venting combustion gases. I would love to tell them it is OK to use these materials, but health and safety trump saving a few bucks on pipe material.

PVC flue pipe failures

Recently, I received a call from someone on behalf of a woman who had suffered a serious debilitating illness. The caller said a plumber gave him a copy of the May 2011 article. The caller went over some of the comments that were addressed in the article and explained that a woman had become seriously ill and permanently disabled from what is believed to be exposure to the combustion gases from two failed PVC plastic flue vent pipes in her home.

I was asked to inspect the installation. I photographed, took temperature recordings and used a multi-gas detector to take readings. The two PVC flue vents were connected to two water heaters that were piped together in the garage of a three-story townhome. The plumber had found that the flue pipes in separate joist spaces were completely separated and that what appeared to be carbon monoxide poisoning and oxygen deprivation may have caused the woman’s illness; she apparently has brain damage and is now permanently disabled.

In exposed locations, the PVC pipe was tan colored; above the drywall and below the second floor decking in the area of the break, it was a very dark brown. Dark areas on the decking and floor joists indicated that high temperature flue gases had possibly cooked the sugars or sap in the wood to a dark caramel color. Apparently, the ambient air had a cooling effect on the pipe in exposed areas; that is why the exposed pipe was a lighter brown color. In the floor cavity, the temperature on both sides of the flue pipe wall was the flue gas temperature. Wherever the pipe was near a floor joist or near insulation, the piping appeared to be darker in color. This was probably because of the restriction of ambient air circulation for cooling.

The pipe was brown and discolored in the vicinity of the two water heaters, and two yellowish fittings were cracked and completely separated. Testing the flue gases in this case revealed that flue gas temperatures after the dilution air was added was still much higher than the 160 F hot water temperature and far in excess of the temperature rating for PVC pipe. The water heater manufacturer's literature recommended the use of PVC pipe and made no mention of system design temperature limitations or installation requirements for the PVC flues with respect to the location in a concealed space or adjacent to insulation. It also did not list any temperature limitations for a maximum thermostat setting on the water heater for systems using PVC flues. The PVC flue pipe separations above the drywall ceiling allowed products of combustion, including carbon monoxide and water vapor, to vent under positive pressure into the house over several years. This caused excessive mold and water damage to the structure.

There is not much data on discoloration of PVC pipe or on ambient air cooling requirements for PVC flue pipes. It appears that PVC flue pipes should not be located in concealed spaces such as the space between a ceiling and a floor deck, near insulation or floor joists or in wall cavities that have no ambient air cooling capability.

There is no standard for PVC pipe for use as a flue material for combustion gases and there is no testing for these conditions.

The discovery

When the home was being sold, an inspector found significant water damage in the lower levels. A plumbing contractor opened the drywall ceiling on the lower floor and found the two completely separated PVC flue pipes pumping carbon monoxide and moisture into the home. There was black mold throughout the floor space and on the exterior walls, where the wood structure and siding was rotted. Copper plumbing pipes in the area were green with oxidation from exposure to the moisture. The broken PVC flue pipes caused the plumbing contractor to wonder whether the building occupants had experienced any symptoms of carbon monoxide poisoning. These symptoms include the following: headaches, dizziness, nausea, flu-like symptoms, fatigue, shortness of breath, impaired judgment, chest pain, confusion, depression, hallucinations, agitation, vomiting, abdominal pain, drowsiness, visual changes, fainting, seizures, memory and walking problems. Not knowing her condition, the plumber contacted the homeowner and asked whether she had experienced any of these symptoms.

She was amazed to hear this, because he was describing many of the symptoms she had been experiencing for several years. These were the reasons she had to quit her job and move away. Moving away very likely saved her life.



Interestingly, although the CO levels were elevated to dangerous levels, they were not high enough to trip a carbon monoxide alarm. The combustion gases that were venting into the floor space and coming up through a floor register into the living space had oxygen levels that dropped to well below 18 percent in some areas. Low oxygen levels combined with elevated CO levels can be a deadly combination and can lead to brain damage.

Flue gas temperatures

PVC pipe has a temperature limit of 140 F; most water heaters and boilers have thermostats that exceed this temperature. Furnaces can have flue temperatures well above 140 F when the air filters are dirty and the air flow drops off. The maximum temperature setting for residential water heaters is 160 F, for commercial water heaters it is 180 F and for boilers it is 200 F, all above the maximum recommended PVC temperature of 140 F. Boiler water temperatures are typically in the 180 to 200 degree range, because most HVAC hydronic heating coils are designed for these higher water temperatures in order to reduce the heating coil sizes and to reduce the gpm pumping requirements.

Plumbing engineers typically design hot water systems to store hot water about 140 F in water heaters to minimize Legionella bacteria and other organic pathogen growth in the hot water tank. They typically use thermostatic mixing valves conforming to industry standards to reduce domestic hot water temperatures to safe delivery temperatures.

If a fuel gas appliance was 100% efficient, the flue gas temperature would be the same temperature as the thermostat setting or fluid temperature in the water heater or boiler. Since 100% efficiency is not really possible, all flue gas temperatures will exceed the thermostat setting. So, if a water heater is set at 160 F and the thermostat allows the fluid temperature to overshoot the set point by about 10 degrees F plus or minus, the flue gas temperatures on a very efficient residential water heater would be higher than 170 F. This is consistent with the temperature readings I got.

Water heater storage temperatures

I serve on an industry committee that is developing guidelines for minimizing Legionella in building water systems. The committee includes representatives of ASHRAE, ASPE, water heater manufacturers, plumbing designers, CDC, EPA, several pathologists and microbiologists and many other experts. They have recently tentatively agreed that the minimum storage temperature for water heaters should be 140 F in order to make sure that all parts of the domestic hot water system are well above the ideal growth temperatures for Legionella. The committee is also looking at minimum hot water return temperatures above the ideal growth temperatures for legionella bacteria. When this standard is published, storage type water heaters will have minimum storage temperatures of 140 F or higher; flue gases are typically much hotter than the water temperature.

Because of the excessive temperatures of flue gases, PVC pipe manufacturers do not recommend the use of their pipes for venting combustion gases and have the following temperature limits for piping materials:

PVC Schedule 40 140 F

ABS Schedule 40 160 F

CPVC Copper Tube Size 180 F

CPVC Schedule 80 200 F

PolyPropylene High Temp 230 F

Stainless Steel 1,000 F – 1,400 F

Why PVC material?

Water heater, boiler and furnace manufacturers have gone to great lengths to promote and use PVC plastic flue pipes in applications that exceed the temperature ratings of the product. They cannot use traditional galvanized flues because the condensation produced is pure water and very aggressive and would corrode or rust the flue in a very short time. When galvanized steel flues develop rust holes, people may start suffering from carbon monoxide poisoning. Manufacturers needed to come up with a flue material that would not corrode. Stainless steel flues are an option but, compared to galvanized steel or PVC plastic, they are very expensive. High-temperature plastic flues were used briefly in Canada but were recalled after a series of flue failures. In the beginning, flues were cobbled together out of whatever flue materials they could find and PVC was included even though it is not rated for the system temperatures commonly experienced in flues. Water heater and boiler manufacturers began listing the ASTM standard numbers for PVC DWV pipe and PVC water pipe as the material to use for venting their appliances.

PVC pipe standards



The ASTM standards, PVC Schedule 40 DWV Pipe & Fittings — ASTM D 1785 and ASTM D 2665 have language as follows:

This standard specification does not include requirements for pipe and fittings intended to be used to vent combustion gases.



The cost of PVC plastic pipe cost is a fraction of the cost of stainless steel. I am guessing that there was a meeting after the May 2011 article and that AHRI decided to defend the use of PVC plastic for venting combustible gases.



The AHRI representative agreed that no U.S. PVC pipe manufacturer recommends use of their pipe for venting of combustible gases. He then goes on to mention that AHRI uses the ANSI Z21 series of standards for appliance testing as the basis for acceptance of PVC flue piping. These standards only test for deflection at 157 F, although he claimed that they test to 158 F. That is not the correct temperature for PVC piping.



He states that the Z21 series of standards tests gas appliances for extreme conditions. According to him, the test involves setting the thermostat to the highest setting and flowing water continuously to keep the burner on. In this condition, enough water can be flushed through the water heater or boiler to keep the water temperatures low enough to keep the flue gases cooled and relatively low. The test does not allow real-world conditions in which commercial water heaters reach the shut-off temperature of 180 F.

To be accurate, just enough hot water should be flowed to cause cold water to enter the bottom of the heater and cause the burner to come on; then the flow of water should be shut off until the burner shuts off. Repeating this step about five or six times would be the real-world extreme condition. Each time the water heater cycles, the hot water rises to the top of the heater; each consecutive cycle overheats the water in the top of the heater and, with each consecutive stacking cycle, the water temperature will be 5 to 10 degrees hotter. As the water temperature gets hotter, so does the flue temperature.



The test does not test for long term thermal cycling of the PVC pipe where the pipe becomes discolored. The test does not address all of the things that can cause flue gas temperatures to rise — scale on the heating surfaces; dirty air filters; insulation, drywall or studs against the pipe in joist spaces; partially and fully blocked dilution air inlets; etc. I would like to see a manufacturer provide a copy of testing and certification for any fuel burning appliance with PVC pipe testing for these conditions.



According to the AHRI representative, the ANSI Z21.10.1-2009, CSA 4.1-2009 Standard, Gas Water Heaters Volume I, Storage Water Heaters With Input Ratings Of 75,000 Btu Per Hour Or Less tests and approves PVC pipe for use in water heaters, but the standard only references PVC pipe deflection at 157 F. It does not address or require the appliance to shut off if the 140 F limit is reached. The only place that PVC is addressed is in Table XII, which gives the maximum allowable temperatures of typical nonmetallic vent material used in water heaters. There is no justification for the 157-degree temperature, which exceeds the piping manufacturer’s temperature rating. Table XII is as follows:



There is no testing for a water heater, boiler or furnace that has a system set at the upper temperature settings with a build-up of scale on the heating surfaces or with a plugged air filter.

Scale is an insulator



Scale on heating surfaces and higher system water temperatures that increase scale production are not extreme cases but are normal conditions expected over the life of a water heater or boiler. The AHRI representative states in his letter that scale is not an insulator. I strongly disagree. Numerous documents, research reports and papers address the insulating effects of scale formation on the heat transfer surfaces and the waste of energy associated with scale on heating surfaces. The insulating effect of scale on water heater and boiler heating surfaces results in increased flue gas temperatures. Scale also causes a substantial waste of energy.



Scale deposits occur when calcium, magnesium and silica, commonly found in most water supplies, get cooked onto the heating surface and form a continuous layer of material on the waterside of the water heater or boiler heat exchanger surfaces. Scale creates a problem because it typically possesses a thermal conductivity, an order of magnitude less than the corresponding value for bare steel. Even thin layers of scale serve as an effective insulator and retard heat transfer.



The National Institute of Standards and Technology, Handbook 115, Supplement 1 addresses the loss of efficiency based on scale formation. On well-designed natural gas-fired systems, an excess air level of 10% is attainable. An often stated rule of thumb is that boiler efficiency can be increased by 1% for each 15% reduction in excess air or 40 F reduction in the stack gas temperature. The efficiency of the equipment decreases about one percent for every 1/64-inch layer of scale on the heating surface. The result is overheating of the water heater or boiler tube metal, tube failures and loss of energy efficiency, which is commonly diagnosed by an increase in flue gas temperature.



Fuel consumption increases as scale deposits increase. Water heater or boiler output will be reduced as the scale builds up. The flue gas temperatures rise, and the burner stays on longer in order to transfer heat through the scale and the heating surface. Energy losses and increased flue gas temperatures are a function of scale thickness and composition.

Where is the data?



A flue pipe should not be allowed to fail and cause an injury or death from a normal system temperatures, location of a flue in a concealed space, or a normal build-up of scale on the heating surface. This is a serious life safety issue that the appliance manufacturers apparently would like to sweep under the carpet.



At the ASHRAE show in Chicago, I asked every water heater and boiler manufacturer that was exhibiting PVC flues on their equipment to show me any testing data they might have that shows the PVC material was not going to exceed 140 F. Some looked at me like deer in the headlights, others rolled their eyes, and a few said they didn’t know and suggested I talk to “that guy over there.” The guy over there did not know either. A few said, “Yeah, everyone’s using PVC now, and I have never heard of a failure.” Not one manufacturer could produce any technical data or a report addressing the temperature limits that the fuel burning appliance manufacturers are required to have for non-metallic PVC flue materials. There are acceptable non-metallic flue materials such as high temperature polypropylene and new, high temperature plastics that have higher temperature ratings than PVC.



The fuel-fired appliance manufacturers, in their quest to use PVC pipe as an inexpensive flue material, realized that no piping manufacturer was going to go out on a limb and certify their pipe for use as a flue gas material, so a proposal for a code change was submitted to the International Fuel Gas Code to allow an exception for the listing requirements for flue gas materials. The exception allows for non-metallic flue materials to not be required to be listed for the application if the manufacturer of the equipment certifies their equipment for use with non-metallic flue materials. They are claiming that they have a certification test, but the test that the AHRI representative cited does not test for the proper temperature limits for PVC pipe. I would be glad to show them how to set up a realistic test.

No PVC flue pipe standard



The AHRI representative went on to talk about dilution air being mixed with the flue gas temperatures. This dilution air is often drawn into the water heater through openings in a hood on top of the water heater. It is a function of the size of the combustion air fan which, in many cases, is located on the flue outlet so there can be a negative pressure zone on top of the water heater where dilution air can be drawn into the flue. The dilution air imposes an additional CFM demand on the unit that is not covered in the manufacturer’s installation data. There is rarely manufacturer’s data on what the fan CFM is and how that affects the combustion air requirements for the water heater or appliance. If there are two appliances located in the same closet and both rely on cooling air mixing with the combustion gases, where are the additional requirements for combustion air openings and dilution air requirements? If a closet or space is designed for only enough air for the combustion requirements, and the hood is drawing many times more cubic feet of air than the combustion air requirement from the same space, the burner can starve, and improper combustion can cause soot conditions that will increase flue temperatures. Improper airflow to the closet or room containing the high efficiency equipment can starve the dilution air ports reducing the cooling capability of the dilution air that is intended to help cool the combustion gases. High ambient air conditions can also cause ineffective cooling of the combustion gases.

Require proof or reject PVC as a flue material



Until any fuel burning appliance manufacturer can produce an independent engineering lab test report that shows that the appliance will shut down if the flue gas temperatures exceed 140 F, an engineer or the inspector has every right to reject the PVC flue materials as not being in compliance with the requirements for listed flue pipe materials in the International Fuel Gas Code.



Fuel burning appliance manufacturers should change their installation literature to prohibit PVC pipe and fittings. They should require other more suitable high temperature non-metallic pipe materials or stainless steel flue materials. They should also address all of the thermal expansion, ambient cooling and stress cracking issues with non-metallic systems. A consensus standard for non-metallic flue venting systems is really needed now if they are going to continue to promote the PVC material.



The manufacturers and AHRI have created an unsafe condition by lobbying for a material that is not suited for this application. They should issue a recall letter to every business and every homeowner that has PVC flue pipes installed on equipment designed for non-metallic flue pipes if the equipment does not have temperature sensors or limit switches in the discharge flue that shuts down the burner if the flue gas temperatures exceed 140 F.



Data also needs to be published showing the dilution air requirements at the maximum possible ambient air conditions. Recent weather events in Southern states have shown that ambient air conditions can get close to 115 F or higher. With combustion gases close to 200 F, you would need a pretty big combustion air opening to bring in enough 115-degree cooling air to bring the temperature down to a safe level.

The decision to use PVC pipe for venting flue gases is purely a monetary decision; it totally disregards public health and safety. The International Fuel Gas Code exemption for non-metallic flue pipe materials is not safe and, in my opinion, should be repealed as an emergency code change. I also feel that manufacturers should immediately discontinue recommending the use of PVC pipe for venting combustible gases.



Ron George is president of Plumb-Tech Design and Consulting Services LLC. He has served as chairman of the International Residential Plumbing & Mechanical Code Committee. Visit [u][color=#0066cc]www.Plumb-TechLLC.com[/color][/u], e-mail [u][color=#0066cc]Ron@Plumb-TechLLC.com[/color][/u] or phone 734/755-1908.

ChrisJ

power vented tank heaters

As a homeowner and not a pro I may be over my head on this but I'm assuming this issue also includes tank water heaters which are power vented.  I have to assume so being it has a burner and can obviously have a failure which would increase temperatures.



Last fall I installed a Bradford & white heater which of course recommended PVC.  My point would be the PVC connects to the heater via a soft rubber adapter which connects to an ABS plastic blower. I don't know what the rubber adapter is made from but its not silicone.  They also supply a outside partial elbow which has a wire mesh screen in it which is molded out of white PVC.  I don't know about others but I would feel a bit stupid connecting stainless pipe to an ABS housing using a rubber adapter.  The outside screen would be another issue as your obviously not going to glue the supplied one onto stainless.

Ron George

The right material.

I tested a water heater recently with a black plastic collector on the top and it had an external temperature of 188 F (downstream of the dillution air inlets) using an IR temperature sensor.  The internal temperature was probably much higher.  When a water heater heating surface fouls with scale the flue gas temperatures will increase significantly.  A burner shut-off using a flue gas temperature sensor that is rated for the flue materials is needed for non-metallic flues.   PVC flues should not be allowed because most appliance or equipment T-stats exceed the material temperature rating.

VictoriaEnergy

PVC can work fine

The simple answers are: 1) All appliances using a plastic vent system, and/or, an uninsulated vent system with low or zero clearance to combustibles, must include a manual reset high limit switch in the vent outlet.  2) Adopt a similar, if not parallel standard to ULC636 which clearly establish the maximum continuous and intermittent peak temps the material has to tolerate.



Our company has been installing PVC venting on warm air furnaces since 1993.  This material has worked well on furnaces.  Not surprising since the flue temps are often in the 100~120F range.  All of the old equipment I can think of had a thermal limit switch mounted in the outlet of the inducer.  Much of the newer equipment seems to have eliminated the switch (tisk tisk).  We inspect PVC closely on every service call and the odd issue we've seen appear are in joints that have no evidence of primer being used in them before cementing.



I think the room air flue temp dilution design is problematic, and the HWH manufacturers would have to walk away from the design if the were mandated to comply with the above.

Limamikemike

s636

Came across this:

http://safetyauthority.ca/sites/default/files/Plastic_Venting_D-G5_070628_5_Rev_3.pdf



Basically says No PVC on anything other than forced air furnaces vents-dated march 8/2012 in canada. Interestingly it says this directive OVERIDES manufacturers instructions.



I recently installed a Lochinvar WHN110 with B11A PVC vent material in a low to mid temp app, the Lochinvar manual states ULC-S636 in canada, either PVC or CPVC so long as its ULC cert. Also the wall thimble included with the boiler is made from ULC-S636 B11A -65c material.



In your eduated opinions should I recall and change it? It passed inspection as is on April 27/2012.



ULC-S636 BIIA -65c flue PVC-White pipe



ULC-S636 BIIB -90c flue CPVC-Grey pipe.

VictoriaEnergy

Responding to the directive

LMM:

It looks like your situation is a good example of the issue the inspection authority is having a problem with.  The instructions for the boiler accept the use PVC,  The B11A-65C is certified for operating temp of 149deg F(65 deg Celsius), but the manual states :



 

The control module monitors the flue temperature by a sensor located in the flue exhaust. If the flue temperature exceeds 215°F the control will reduce the maximum fan speed. If the flue temperature exceeds 240°F the control will shut the unit down. The unit will restart automatically once the flue temperature drops 25°F and the minimum off time has expired.





So although your system is probably running flue temps well below the limit of the vent today, what happens in a few years if the unit is not maintained the hx gets scaled up full of crud, and the flue temps creep up?  If you have indirect HW on the system, it’s reasonable to see the boiler frequently overheating the vent.

 

As far as your customer goes, (assuming the notice is for your area) I think you have to contact them and advise the installation needs to be upgraded.  They won’t have an issue with you tell them they need a new vent, but they likely will want to talk alot about who gets to pay for it.



  If you started the job before the directive was issued, you’ve done nothing wrong.  The upgrade materials and labor are chargeable.  I’d send them a copy of the directive, the phone # of the inspector, and tell them they are not obliged to have your company do the upgrade, but they must have it upgraded.  Out of sympathy and in the interest of good customer service, I would offer it to them at my cost if they were willing to do the upgrade during the summer when my work load was minimal.

 

If you remember the job well enough, you can include a complete quote for the fix.  If you have previously delt with them via e-mail, I’d 1st communicate that way.  Wait a week and contact them again.  If they refuse to take action, claim to be hiring another gas fitter for the work, or won’t communicate further, forward all the info to the gas inspector to show him you tried and won’t be taking further action.

Ron George

Reply to Mark E.

Mark E. Wrote:  1. It sounds as if the actual failure was possibly stress induced due to the high coefficients of expansion common to PVC plastic? If yes, would an expansion joint have alleviated this stress and avoided pipe/fitting failure?

Ron's reply: The pipe was not restrained.  There is no PVC pipe or PVC expansion joint listed or approved for venting combustion gasses.



2. Was the appliance doing only DHW, or was it also doing space heating and DHW?

Ron's reply: Boiler manufacturers, water heater manufacturers, furnace manufacturers and manufacturers of equipment intended for both space heating and domesti water heating all have literature recommending the use of PVC materials for the flues.  The thermostats on all these appliances allow discharge flue temperatures which are above the allowable temperature limit of 140 established by the PVC pipe manufacturers.

 

3. What is the status of your patent pending flue temperature control device?



Ron's reply:  I let it lapse.  No patent.  This is a safety issue not a monetary issue.



4. Why no mention of ABS in your articles? 

Ron's reply: No reason.  ABS has a temperature limit of 180 F.  !80 may still be questionable is many applications where the temperatures can easily exceed 180 F with scale build-up on the heating surfaces.



5. Are you aware that long term exposure to Black Mold will also produce many of the symptoms that the resident of this home has experienced?

Ron's Reply:  In this case it is clear the black mold was caused by the failed PVC flue pumping warm moist air and combustion gasses into the joist space.  What is your point other than to defend the use of PVC for venting combustion gasses. PVC is an inapropriate material for this application and the underlying reason is to save a couple of bucks?  In either case a person can become very sick or die because of a failed PVC flue pipe.



6. If you feel that the Lignin had been cooked out of the wood due to the close proximity of the PVC to wood, what do you think the chances of pyrolysis would have been at an elevated wall surface temperature associated with highly conductive, low thermal resistance stainless steel would have been?

Ron's Reply: The stainless steel is a double wall system so your comments about radiation are irrelevant.  The flue gasses were directly impenging on the wood with convection currents from the broken PVC flues.  In a double wall stainless steel flue system with proper clearances or with a properly designed and listed non-metallic flue system the external temperatures should not get high enough to cook the sap out of the wood. 



Lastly, as an expert witness, do you think it ethical to bring this situation before the public prior to finalization of any potential litigation being closed out? You know, there are a LOT of legal beagles who frequent this site...

Ron's reply:  I have not disclosed an address or names.  I have been speaking in generic terms.  This is a serious life safety issue that people need to be made aware of.  Safety is always my first concern.  Safety should always be more important than saving a few bucks on a material that is not intended or listed for an application.

JohnHenry_2

Mr. George,

Having been trained as a mechanical engineer, I'm not feeling real warm and fuzzy about your comments here. You seem to imply that the engineers who design and test these systems have little regard for the safety of consumers. Nothing could be further from the truth. Engineers care very much for the consumer and are generally insistent that the systems they design are pretty much bulletproof.



While I applaud your apparent desire that all heating systems be immune from reckless and unqualified installers, zero maintenance and general neglect, in the real world that's just not going to happen. One of my favorite sayings is: "if you build a better idiot trap, they'll build a better idiot".



When a company designs, manufactures and sells a system, they have the right to expect proper and competent installation of their product. Indeed the literature that invariably comes with said products states that it must be installed correctly.



Like it or not, cost does matter. If you can get adequate performance from a cheaper material, you use it. Period. That's just the way it is. EVERYTHING has a cost benefit analysis attached to it, from how much you spend on flowers when you piss off the wife to what material you're going to use to vent a combustion appliance and everything in between. Would you ballast a sailboat with gold?



Let's get to the PVC, shall we?



ASTM Type-1 PVC standardizes schedule 40/80 PVC with:

a melting point of 360*F

a continuous service ambient air temperature rating of 160*F @ 264psi (temperature rating goes up with less pressure)

a deflection temperature of 154*F @ 264psi (temperature rating goes up with less pressure)

a Rockwell hardness of 112



That's a very simplified example of the type of data an engineer looks at when choosing material to approve for venting. The engineer will use temp/strength curves to determine the maximum temp a material can take before it deforms in the use and layout it's installed in (in this case probably 1 in WC pressure, laying horizontal with support every 5 ft). They then see if that temp is within the bounds of the intended operating range (with a generous factor of safety of course) of the application.



My particular condensing appliance allows a maximum 149*F flue temp before it shuts down. My system return water has never run above 120*F. I've never measured the outside temperature of my flue to be more than 105*F. Given these running parameters, the PVC that I carefully and correctly installed will probably never leak, corrode, give off fumes or genarally cause me any trouble. How is that not the right vent material for me?



There are vast numbers of condensing hot water heaters/boilers running PVC venting without any venting issues. It seems that PVC can indeed be an appropriate venting material.