Hello everyone, 

   I encountered a propane water heater with an assistance fan right on top of the unit, vented with Poly(Vinyl Chloride) (PVC) Plastic Pipe, Schedules 40. The vent is obviously hot and it shows color discoloration... I need verification that this is a correct or incorrect way of venting this water heater since I cannot just go by feeling. So far I found on the web the normal stuff, that it is used for pressure rated for water situations. Any documentation out there that you could share please?


Tags: PVC, heater, venting, water

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There is a burned mark on the right as well. That pipe was at 180 when I was there

This really looks like burn marks when someone replace copper fittings to the right of the vent.  It also looks like they used CPVC for the first six inches before moving to ordinary PVC.  That could also be why you see "yellow" pvc instead of all white.

How did you measure the pipe temp?   IR camera?   That white pipe will reflect other heat sources that are near it.  The emissivity of the material would need to be allowed for.   A contact thermocouple?

How hot is the temp of the draft blower that the pipe is coming out of... Is the motor running HOT (as in failing).... you may want to check the air flow out of the vent pipe and check the temp and flow rate.  As others have noted - if the flow rate is low...you could have a blockage

That black spot looks to me like someone was sloppy with their torch while working on the copper pipes and burned the PVC.

The first pipe does look like CPVC I do not recall seeing CPVC listed as approved vent in any instructions. The way PVC cement works is it melts the two pipes and when the glue dries the pipes are fused into one piece.  Since PVC and CPVC are different I an not sure they can fuse properly.


Given that this job is such a hack up mess the safe bet is to recommend it be replaced.

Jose Macho adding a screen that was not approved by the heaters manufacturer is a very risky play. Under certain weather conditions the vapor in the exhaust could freeze onto the screen and restrict the flow in a way the manufacture did not test for. How would you live with yourself should someone die? The manufacture likely tested for infestation and decided no screen was safer  


I don't think he needs to worry about the vent.  I think he saw what appeared to be yellowing pipe and a possible burn on the pipe and was concerned.

CPVC has a higher temperature rating than ordinary PVC.  Often around 180F under pressure.  I suspect the installer - (years ago) used the CPVC for the installation because next to the blower the temps are hotter and less deformation..   But CPVC is more expensive, the they used as short of piece as possible.

Rinnai has instruction which show the use of PVC or CPVC used for vent pipes.  


I have seen too many vent pipes with no screens which invites infestation & nests. This can cause partial air blockage which will affect combustion. Use a combustion analyzer to measure CO, Excess Air & efficiency at the outside exhaust vent. Outside can be separate pipes or a combo intake/exhaust grille. If you pull the unit cover off to inspect make sure it is put back correctly on the gasket for a airtight seal. Some of the manufacturers now require higher temp rated poly which is gray rather than sch. 40 white.

35 yr ago We used CPVC for the 1st poly fitting on all 3 maker of 90%.   Must look at flue gas meter if not just wasting your time.    Be a pro and use a flue gas meter  as low as $550 tells CO, temp, o2.  In late 80 we used wet cans and took lots of time now just drill a small hole in flue and test from cold start up to full on to cool down, We just took 13 flue gas meters and turn all on at same time then put 100 PPM CO in a small can out side  and went from 81 to 112 PPM.   

The wording from one of Luis's post on April 20th, seemed to imply that the heater was a boiler not simply a water heater.   If the temp measured was using IR point&shoot measurement - my guess is the 180F reading was either reflection or the field of view included the boiler tank/copper pipes.

I'm not sure he has a problem.  At 180F the elbow above the CPVC would have been showing signs of distress.... it's not.

Something is wrong

Hire a professional technician that knows the equipment & get it checked. 

No idea.

looking at the photo which we most likely could use a pic above that fitting

Someone just above suggest that the burn mark looks like from a torch I agree

It is in line with where the copper line was sweated

Discoloration looks normal to me put a bit of heat on pvc and it yellows

the black band and  PVC connection not liking what I see there with the glue. That looks sketchy glue looks fine in the fitting above it 

I suspect there is a specialty glue for the two different materials and something that resists the heat. It looks like abs but hard call to make a thousand miles away and on the other end of a screen. Again do not like how that glue looks

I would recommend replacing the pvc due to the apparent torch mark that has damaged the pvc to an unknown extent.

I would call customer service of the water heater have pictures and ask if the black fitting is a transition fitting from manufacturer and if so price and availability part number for customer and if there is a recommended glue to bond the two different materials

If it is not from them recommended material for that transition and installation guide

I would provide those answers along with a customer service number for the customer

recommend customer contact a contractor that specializes in these type of units for proper repair

That is how I would play it if it were my audit

Can't say that surely but you can ask the professionals for that. You can ask your queries, see here for more information. And be sure about the whole situation.


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