Perry got me wondering,

Unknown

his data on CPVC & PVC chloride corrosion within a HX, is there a simple way to calculate how much is finding it`s way back-in? Or should a drain tee routinely be installed(pointing down of course), like was suggested by another poster. <BR><BR>I mean, how much condensate would separate within the SS HX and go to drain(never see the piping), and how much rolls back from the vent piping?<BR>Also, on a Prestige, isn`t the HX above the drainage point so how could this get back in?<BR>Or perhaps I just answered my own question?<BR><BR>Dave

Unknown

David, I do not

adhere to pitching the vents back toward the heating system (I am known for operating outside the box on occasion) as manufacturers recommend. I pitch toward the outdoors and use a trap on the flue gas pipe. I have seen them ice up no matter which way you pitch but I would rather have condensate away from the boiler.

It is impossible not to get some corrosion from acidic condensate by the way no matter what you do. I have over 50 years of looking at the combustion and water side of systems and can tell you no one is going to solve that problem with metals being used no matter how non-ferrous they are.

Unknown

OK Tim,

but what about a scenario(like mine), where the existing masonry chimney(up-through the house) was used as a raceway?
Perry made such a "big deal" out of it, I just thought I would ask.
Thanks

Dave

Perry_5

What Perry is looking at on this issue

Dave (and others):

I've been trying to find information on the net concerning the rate of leaching from PVC and related plastic pipes.

Most of the stuff a search finds relates to various softners, etc, leaching into water pipe (and some polyvinyl too) - and a lot of issues with potable water contamination or corrosion caused by the trace chemicals leaching. That has enough differences that I do not consider it directly comparable to boiler exhaust vent piping.

Here is what I know so far:

The leaching problem is worse as the temperature goes up. This is why hard PVC pipe is approved for cold potable water but not for hot potable water in many places in the US.

It appears - based on limited references comparing the two materials - that CPVC has a lower leach rate than PVC as it withstands higher temperatures better.

In test conducted on chlorides in the air vs chlorides in the condensation from condensing furnaces/boilers it was found that with a 1 ppm chloride level in the air that there was a 26 ppm chloride level in the vent condensate. How much of that was from a PVC or CPVC vent pipe I do not know at this time.

Pure water is known to leach stuff from PVC pipe faster than normal potable water. Exhaust gas vent condensation would be highly pure (distilled) water.

That's what I have found so far - with no good source on detailed numbers in a direct fashion to address my questions.

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I will continue to poke at this. Keep in mind that I do this part time and I'm trying to avoid having to spend money buying research papers.

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Concerning the Triangle Tube Prestige:

The material is not succeptable to chloride induced Stress Corrosion Cracking like the 300 series SS's are. It is however succeptable to chloride and other forms of pitting.

The HX is constructed in such a way that drainback from the vent system would not get directly into the body of the HX; however, the boiler HX includes the drain pan for the condensate - and the drainback from any vent system will get into that drainpan. Thus - the lower drainpan is succeptable to pitting from chlorides (and other things). I also worry that if you have natural gas or propane with the "wrong" trace elements/contaminants that you could get burner deposit pitting in the HX tubes as well.

Of course, I cannot say how long it would take for problems to develope - if they develop. It is possible to construct a vent system that directs most of the vent system condensate away from the boiler.

Hope that helps.

Perry