[FONT=Calibri]Hello all,
I thought this would have been posted already but I couldn’t find anything. I see rust on water heater flues all the time. This particular one is in a two year old house that was never occupied. It is surface rust on the outside.
Is there a solution to this issue?
Any idea what is causing this?
Thank you for your help! [/FONT]
(1) running acidic condensation from combustion gases- too low flue gas temperatures
(2) rain entry
Storm collar on the roof/pipe not sealed?
Looks like carbon dioxide and water mixed into carbonic acid from the condensing of the exhaust gases or mixing with other water (missing cap?).
Maybe the water heater was set on “vacation/low”, or for some other reason, the exhaust had opportunity to cool before it left the vent pipe.
Good answer
I never did like those bull headed Tee fittings much prefer the wye the Tee’s give the flue gases a chance to slow and condense and create just what is shown in the PIC 
Had one similar the other day a 90 allowing the gases to cool and create rust
It is very possible the flue gas cools before exiting. The water heater was set to low. The b - vent extends through a lot of cold attic space (about 7 feet) before exiting (Wisconsin).
I checked the storm collar and it looked good.
Thank you
So this is probably rusting from the inside out?
Prolly:) See Larry is pretty smart for a Yankee;-)
Thank you all
I learned something tonight
Here is some more for ya,contractor recently installed this one and as usual wrong was not the home owner the furnace was an 08. I know this contractors work always something wrong.
Is that a water heater and a furnace flue across from each other?
Yes and one is gravity and one is not:roll::roll:
Do the guys that can’t read manufacturers’ instructions, codes and understand better practices always get shipped to the HVAC field?
WOW!:shock: