When we replace an existing FAU, and connect with single wall pipe, and connect to a transite pipe, water will pour backwards into the furnace and flood the controls. Often, there is an oily substance that comes down the pipe. At one time I thought the customer stored a can of motor oil on the furnace and the can leaked. It looked exactly like 3-in-1 oil. Most people think their roof jack is leaking, but these leaks occur when we haven't had rain in over a leak.Flue gasses condensing in the flue. for non condensing appliances the flue gas must be above 400 degrees. Long flue runs will also cool the gasses and cause the problem.
When we replace an existing FAU, and connect with single wall pipe, and connect to a transite pipe, water will pour backwards into the furnace and flood the controls.
I probably know it by another name, but what is transite?This is the reason we aren't allowed to vent back into transite....Some manufactures also advise venting into transite.. When I run into transite . I line it with DW vent.. If it's oval transite.. I install a 90+ furnace
Size your venting properly. Too large and you won't get a proper "stack effect", the gasses will cool off and condensate inside the vent. End result? New Furnace.
No its not a 90% furnace as any body in the HVAC industry can plainly tell from the posts.Out here in De. we are allowed to use Pvc for the High 90% over above. I am gathering that is the type of heater in use. If that is the case, then, there sounds like you have a pitch pblm.