Fernco on direct vent from condensing water heater

[jtech1]

I am finishing the installation of my Phoenix power vent condensing water heater. I have a question about the vent connections to the unit. I see a lot of pictures online (and on these forums) where people have used fernco connectors to connect the intake and exhaust to the unit cpvc stubs. I would like to do it that way, but I don't see anything in the manual that says this is ok. Are they special fernco fittings or just regular plumbing ferncos? Thanks!

https://goo.gl/images/s7mjGd
https://goo.gl/images/gKNAXA

 

[Reach4]

The couplers in your photo are not used for regular plumbing above ground. For regular drain plumbing, the coupler would be a banded/shielded coupler, such as Fernco 3000-22 or Mission CP-200 for 2-inch.

I am not saying what is OK for that water heater's connections.

In case you are wondering, the metal band can be completely removed and put back on top of the rubber part if that makes installation easier.

 

[Sponsor]

 

[Phog]

I also can't say for sure what is ok to use vs not, but i would suggest that the relevant considerations are temperature range and material compatibility.

A lot of those no-hub couplings are made from neoprene, which is good to roughly 200F. But you would need to check your specific coupling's spec sheet to confirm.

Flue gas condensate has trace amounts of nitric and sulfuric acid (and probably other things as well). I know Fernco has material compatibility charts on their web site, and I imagine other manufacturers do as well. Using a coupling that is not compatible with the flue gas condensate would likely mean that the coupling will slowly weaken & disintegrate over time, like how your toilet flapper eventually falls to pieces from contact with city water.

 

[jtech1]

I did a little more research... fernco couplings are made from PVC... and have the same 140 degree temp rating as sched 40 pipe.
Condensate from condensing direct vent units produces water/carbon dioxide/carbonic acid. This fernco document indicates that they are compatible with carbon acid. So, everything I an seeing says they should be fine... but, I would sure love to see the manufacturer saying that. And someone who is familiar with building code/inspections to weigh in...

https://www.fernco.com/sites/default/files/literature/fernco_acid_resistance_chart_2017.pdf

 

[Reach4]

I did a little more research... fernco couplings are made from PVC... and have the same 140 degree temp rating as sched 40 pipe.

Have a citation for that? I am skeptical.

 

[jtech1]

Second paragraph...
https://www.fernco.com/sites/default/files/literature/Flexible_Stock_Couplings_Submittal.pdf

 

[Reach4]

Second paragraph...
https://www.fernco.com/sites/default/files/literature/Flexible_Stock_Couplings_Submittal.pdf

Yer right. Thanks.

I wonder what the black material for the shielded couplers is.

 

[jtech1]

From what I have seen, the shielded connectors are neoprene... so it may provide more stability (if that is needed) with the shield, but opens more questions about whether neoprene is ok to use. There should not be any weight on the connection anyway... if there is, the pipe is not supported properly. So, I am still leaning toward regular PVC Fernco coupling.

 

[Jadnashua]

If the heating device says pvc pipe is an approved material to connect intake and exhaust, any fitting that is approved for use with PVC should also be okay.

 

[Cacher_Chick]

Off topic, but we are seeing more and more suppliers who have move to cellular core PVC, which is not approved in any of the furnace specs I have seen. Make sure if you are buying PVC that it is solid core.

I don't see any reason to use a flex coupler where a standard PVC one does the job. It's not like the furnace gets replaced every year.

 

[BillTheEngineer]

A call to your local inspector is your safest bet.

PVC pipe and fittings can be used at greater than 140°F, it's just that the pressure ratings are de-rated, even at 140°F it's already de-rated. The max pressure rating is at 73°F I believe. Not knowing what the possible max continuous exhaust temperature is from your boiler/WH makes this possibly an iffy situation. If it's below 140°F I would say it would be okay, above that it would be an issue. Some of the flexible coupling do have higher temperature rating so that may be an acceptable option.

I am aware of other flexible connections that would work, but I doubt any local inspector would sign off on them. Basically it's the same type of hose that is put on a car's exhaust pipe when it is being emission tested or on a dynometer. www.crushproof.com

 

[Bgard]

the venting requirements for any CAT 2 CAT 3 OR CAT 4 appliance is based on the appliance manufacturers recommendations. you will not find ANY PCV OR CPVC manufacturers that approve there product for the use of an appliance vent.