Fernco in furnace vent pipe

[Scott Latosky]

Are rubber Fernco fittings able to be used in high efficiency furnace vent pipes? See picture. Just saw one a change out for a gas water heater too? Kind of interesting have never seen this in at least 10 years of inspection and now have seen it back to back. Kind of how this thing goes.

[Hank Spinnler]

Hi Scott,

If the installation manual were available, I'd want to look through it and see if they specify to use only schedule 40 PVC.

[Scott Latosky]

Thanks Hank. The manual unfortunately was not available but from my experiences most all installations I have been involved with the manual calls for schedule 40 PVC plastic. I had listed it as a potential concern to be evaluated along with a few other issues that were present with the HVAC system.

[Hank Spinnler]

I Googled Carrier high-efficiency furnace installation instructions and came up with a pdf that was generic, but had this. The SDR 26 & SDR 21 refers to PVC pressure pipe.

GENERAL VENTING GUIDELINES

Vent system and combustion air supply components
must be constructed of schedule 40 PVC, PVC-DWV,
SDR26, SDR 21 or ABS plastic pipe, fittings, sealants,
and installation procedures that conform to the
following ANSI/ASTM standards:
PVC ASTM D-1785
SDR26, SDR21 ASTM D-2241
PVC-DWV ASTM D-2665
PVC-DWV Cellular Core ASTM F-891
PVC Primer And Solvent Cement ASTM D-2564
ABS Pipe And Fittings ASTM D-2235
Procedure For Cementing Joints ASTM D-2855

[Scott Latosky]

Thanks Hank. Fernco fittings do not fly on pressurized vent systems. I should have been thinking and made that a little more simple. Just caught me of guard. Like I said not something I had seen in a considerable amount of time inspecting. I guess that is probably why. Thanks for a quick response. That is impressive.

[Bob Harper]

Fernco fittings come supplied by the mfr of some power vented water heaters so you cannot state they are unsuitable for all positive pressure venting. It all falls back on the mfr.

Also be sure you are talking about the exhaust and not intake. There really should not be a problem using one on the intake unless your AHJs are reallly tough like in Taxachoosetts.