Before I begin, I would like to state that I have contacted two different HVAC professionals who have visited my home and provided two different solutions regarding water condensation building up inside the furnace flue vent in the attic.
Below is a brief description of my setup:
I live in a 2300 sq. ft. two story colonial, with a natural gas furnace in the basement rated at 135,000 BTUs. The house is 20 years old and has the original furnace. The water heater and furnace share the same flue vent which extends from the basement, up two stories, where it reaches the attic. In the attic the vent bends at a 45 degree angle towards the back of the house, where it bends another 45 degrees up and out the roof. (I am assuming they angled the vent towards the back of the house so the vent stack would not be visible in the front of the home). At this last bend where the flue vent exits the roof is where water condensation is building up inside the vent and dripping onto the drywall below.
The one HVAC professional explained that the long stretch of vent pipe in the attic from the front of the house to the rear of the house was allowing the furnace exhaust to cool prematurely inside the vent, which in turn was causing the water to condensate and drip from the elbow. The solution he suggested was to wrap the entire vent pipe in the attic with fiberglass insulation to stop the premature cooling of the exhaust and allow the warm air to continue until it exits through the vent stack.
The second HVAC professional stated that this was a normal issue and suggested that due to the age of the furnace and the amount of work it would take to install/repair the vent piping that the best solution would be to install a high efficiency furnace which uses a PVC exhaust pipe through the basement rim board.
Can anyone provide any further insight?
I will eventually replace my furnace with a high efficiency furnace, but both the HVAC pros stated I still have a few years left in my existing furnace. I would hate to throw the baby out with the bath water so to speak, replacing everything because of water condensation in the attic.
Any suggestions or feedback would be greatly appreciated.