Dielectric Fitting

Hey Guys-

Any of you seen a dielectric fitting burn like this? The owner reported that the water heater and all the fittings were replaced in 2009. The flue vented okay with the smoke test and the other fitting had no damage. Any thoughts as to the cause? Thanks.


That is a problem with the water heater vent, not the coupling. Something is preventing the water heater from venting properly. The vent is spilling hot combustion gasses. Your smoke test may not represent the conditions under which this is occurring.

Make sure that there is proper combustion air provision when all doors are closed. Make sure that the vent is properly configured. Look for exhaust fans in the same area, etc.

I would treat this as a high priority safety issue.

I considered that as one of the reasons why the left one was burned but not the right one…that is, the gases had a focused exit point on the left side. The evidence of debris around the base of the flue also would indicate that.

When I did the smoke test I made sure the water heater and furnace were both running and the smoke was pulled right out. The mechanical room was plenty large. Full basement that wasn’t fully finished and the dryer was on the main floor. Only one small bathroom vent which was located on the complete other side of the basement. No whole house fan or other abnormal ventilation system in the home and the appliance vents were in good shape.

OK if you can’t diagnose exactly why during the course of a home inspection. The evidence that a problem exists is right there in your photograph. Don’t let the fact that it worked OK today prevent you from documenting that there has been an issue.

BTW: though I can’t see it all, that doesn’t look like a large area to be pulling combustion air from for both those units (50cf/1000 BTU), as I recall. When natural draft and induced draft appliances compete for combustion air, induced draft wins.

Thanks Chuck. I agree and have called it out accordingly. I guess in my mind I was playing around with the possibility of a bad alloy or something along those lines.