This is taken from the “How to inspect HVAC systems” of the online course. I was wondering if the last paragraph (concerning draining the condensate back to the unit) was a true statement. It seems false to me. Just wondering.
"PVC Pipe Venting
High-efficiency furnaces use PVC piping to vent combustion gases and byproducts outside. You usually see the PVC pipe extending from the furnace through the wall to the outside. A PVC vent pipe will likely indicate a high-efficiency gas heating system. The pipe is typically 2 inches in diameter. PVC is also used to bring fresh outdoor air into the system for combustion. The length could be very long – sometimes as long as 60 feet.
The temperatures of the combustion byproducts are low – 100° F to 150° F. That’s very cool. The PVC does not melt. It will feel warm to the touch. That’s one way to determine which pipe is the exhaust.
High-efficiency furnaces should not be vented into a chimney. The exhaust gases from a high-efficiency heating system are too cool to create enough chimney draft. The cool gases will condense inside the chimney and cause damage.
PVC pipes need a proper slope. The pipe should be sloped down and toward the furnace, or slope up and away from the furnace. Typically, ¼-inch per linear foot is recommended. The pipe should be sloped and adequately supported so that condensate does not form and puddle inside a sagging part of the vent pipe. **The condensate should be allowed to drain back toward the furnace. **