I have a 8yr old American Standard 90% effecient furnace that after the unit reaches it’s preset warm up temp. and starts actually blowing the warm air, shuts off after only a couple of seconds and starts cycling through almost continually. I added 15′ of pvc exhaust pipe to move it from under a deck I built and was wondering if that could have thing to do with it by possibly retarding the exhaust air flow.
