PVC for venting from Viessmann

mitchb

I believe they are addressing the issue of Canada enforcing the BH venting systems requirement inthe gas code.

For years we have used regular PVC and CPVC, but no manufaturer has ever certified to ULC standard 636.

Ipex and others are now producing BH venting to that standard, and is so labelled S636 on the pipe.

The attachment references all the same temperatures, and IPEX and the standard.

We classify the new BH as PVC BH for low temp 65°C, and CPVC high temp.

The main difference is certification. If you check out the system 636 venting, it is very different in feel to regular PVC and CPVC. Any supply house should be able to order a sample if they deal with IPEX.

Mitch

ScottMP

PVC vs CPVC

I received this from a friend who passed it on from Viessmann in regards to the use of PVC. Many of us install mod/cons that allow the use of PVC for venting.

Is this a big issue? Should we be using CPVC on our jobs?

Will this become an issue for jobs we have installed over the last three years??

Scott



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Brad White

That indeed is the current practice

PVC? Nein.

CPVC? Ja.

Polypropylene? Ja. Und ve haf dat.

Personally, I would stick with the manufacturer's own product/system if offered.

Viessmann North America is stocking CPVC pipe and fittings as a convenience as an alternate to their factory co-axial system for when a parallel system makes more sense.

joel_19

pvc

I can see PVC failing especailly when not well supported and glued. At the same time though we 90+ furnasties with no maintenance with plugged filters,blown motors etc banging off their limits etc. I wouldn't loose sleep over it but I would want them them to inspect the boiler every year which should happen anyhow.

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Mike T., Swampeast MO

The issue of PVC venting has been brought up many times. When I try to sort things out, I always encounter a BIG problem. PVC and CPVC pipe ratings are based on temperature and pressure. Even DWV pipe and fittings (which under normal conditions should have almost no pressure) are rated at high pressure. 2" schedule 40 PVC for instance is rated at about 280 psi @ 73F.

The only "pressure" I see affecting PVC heating appliance venting is its' own weight and when I searched for PVC properties it [seems] impossible for a condensing boiler or furnace to produce temperatures high enough to even increase sagging beyond what can occur by its own weight (if improperly supported).

That said, PVC and CPVC both tend to become somewhat brittle over time. This even when buried quite deeply (nearly constant temp) carrying only cold water, and never exposed to the sun. I've noticed this over and over in many different locations and applications. At least it [seems] that the brittleness fairly rapidly (say 3-4 years) hits a maximum and doesn't increase further.

UV (e.g. sunlight) exposure however DOES make PVC (I don't know about CPVC) extremely brittle. I'm certain that's why the grey UV stabilized PVC is used for electrical purposes.

I know PVC/CPVC has never been rated for use with condensing appliances, but something tells me that the structure itself will have to be torn down before PVC fails for "natural" reasons...

Unknown

I have been doing a series of a

articles on this subject for the HVAC Insider Paper over the last couple of months and will be sending one to them this evening on this very subject.

It is really important to get all the facts on what venting material to use as I have seen problesm over the past three years with PVC and even some CPVC vents.

I feel that even a combination of temperature along with the acidic condition of vent gas especially in the condensing mode can have an reactive affect on plastic piping.

It is my opinion we should be venting only with AL294C stainless steel vents. Terminate them 30" or higher above grade. Seperate intake air from vented gases by at least 36". All intake air should be warmed to at least 60 degrees (F). OR use concentric vents.

rich pickering

36\"

"Seperate intake air from vented gases by at least 36". All intake air should be warmed to at least 60 degrees (F). OR use concentric vents."

I'm finding that if the appliance is running at about 35,000btu or less, the outdoor air is about -20 or colder, there is no wind and a concentric is used, there is a good chance of frosting the intake.

The problem is the exhaust does not have enough velocity to get far enough away from the intake and gets pulled back in.

ScottMP

Tim

What problems have you been seeing ? I have yet to see any problems even with older 90+ furnaces. That of course means nothing as I may just not have come across any yet.

But what have you seen ?

As far as the condesates acid nature, we are sometimes asked to install PVC piping for drainage in acidic conditions, even though its a commercial application. The Inspectors feel the PVC stands up to corrosive elements better.

Scott

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tim smith

PVC & longevity on condensing equip.

We have probably serviced 90% furnasty's 1000s of times over the last 18 yrs. We have some that are 18 yrs old I think and that is about the oldest. No signs of deterioration on the flue way pipes. A little yellowed discoloration but thats it. Maybe a little sooted sometimes from the many bad heat exchangers we find. I would have to say that is not too bad of a testament. I would be interested to how close the boiler and furnace flue temps are to each other. I will have to remember to check at full temps of both units. Tim

Unknown

Tim Smith, most furnaces

are bringing on the system blower in 30 to 60 seconds to protect thermal stress on the heat exchanger. That pretty much insures that flue gas temps stay pretty close to 140 degrees or slightly less. On many of the condensing units the secondary heat exchanger is pulling a lot more heat out of the flue gases before the vent sees them so the temps stay below 120 degrees. If you are doing a combustion test on every one of the thousands you service I am sure you have seesn those temps stay below maximum temp on PVC and CPVC. With boiler water temp at say 180 or 190 with a differential of 20 degrees then return water temp is 160 to 170 with a dew point of 135 to 140 that boiler would not condensate and the stack temp would be higher on a consistent basis than the design of PVC or CPVC and ABS.

Unknown

Scott I have seen cases over the last

20 years of softening of the plstic from original consistancy. Testing conducted at my old company of sustained temps on PVC of 180 to 200 degrees (F) showed stretching and expansion beyond allowable specifications. I have recently in the last ten years upon conducting a soap test on PVC and CPVC plastic pipe found that joints leaked and there was evidence when removing the pipe of acidic reaction with glues and solvents used on the joints causeing then to leak. A combination of long term temperatures above the allowable for the plastic in conjunction with the carbonic, sulphuric and nitric acids causes this to occur. In addition if VOC's were present in the environment then this increased the frequency of detoriation. If everyone is doing annual combustion testing on their equipment then you will begin to find some of these problems. The lack of annual tuneups and testing especially on mid and high efficiency equipment will prove to come back on us all as problems and replacement of equipment before its time. This stuff is not your old furnace or boiler it must be checked annually or it will be gone in 10 years or less.

Unknown

Rich it is amazing

that we have been running thoudands of wall hung space heaters for years with direct vent (concentric vents) at between 35,000 to 50,000 BTU's and no problem at all. The reason the flue gases leaving were at a higher temperature. With all the mid and high eff. equipment we are running at much lower temps so we have air intake problems. We have to find ways to warm the air coming into the unit or in extreme conditions pay the price. Hey years ago we hung a couple of 100 watt light bulbs in the boiler and furnace rooms to get a little heat in there.

rich pickering

The problem is that at -20, you can't warm up the air until it is inside the structure. And by then it is too late.
I know concentrics look better, but I like your idea of 36" better.
Look at installation drawings. If there is 3 concentrics, the first 2 have to be 1"-2" apart, but the 3rd one has to be 36" away from the first two.