William Ketel, like many engineers the de facto repair person for his extended family, wonders why a brand-name furnace would feature a shoddy hose:
“I received a call from my dad asking me to come over and see if I could stop the humidifier on his high efficiency furnace from leaking all over the floor. At least, that is what it seemed to be at first glance, since water was running out of the furnace when it ran, and across the floor to the drain. But the closer I looked, the less it seemed to be the humidifier, especially since the water valve to the humidifier was closed and it was dry. So it was time to dig in a bit deeper.
Opening the bottom cover revealed that the water seemed to be coming from inside the blower compartment. At least, that was the appearance, since there was nothing else in that area except a hose from the combustion compartment drain port. This was quite puzzling for a bit, until I got a really bright light and examined very closely. The water was coming from the hose, passing right through its walls when the furnace was running and the combustion chamber was pressurized. The flow stopped instantly when the combustion blower stopped.
Removal of the hose and a close examination revealed many very fine cracks in the wall of the hose, which would allow water to flow through with even a small amount of pressure, but which would close as soon as the pressure was relieved. The solution was to replace the hose, but not with another one of the same material, which evidently did not stand up to the products of combustion found in the drain water.
Since it was a formed hose with a sharp 90° bend at one end, it took some effort to form a replacement, using some high-performance MWPE hot water tubing. The good news is that the replacement material has lasted longer than the original. The next season I had to replace a second section of the failed hose, again using the MWPE tubing.
My concern is that this furnace was a name brand device with a good reputation. How did they wind up using materials that were totally not suited for the application? These were OEM pieces, not parts provided by the installer or patched in by a service person. Why would they take chances in a product as critical as a home heating furnace? Or was it a case of purchasing finding a cheaper source of “the same thing”, when it just looked the same? IT did convince me to consider other brands when I shop for my next furnace.”