agstaff

I've read quite a few of the posts here. I've researched this topic extensively and can't seem to find a definite answer. I've read the tables and performed the calculations. Here is my situation: 80% 66,000 btu fan assisted Bryant furnace, 4' single wall connector, 2 45 elbows, no horizontal runs. 40 gallon water heater, 40,000 btu with natural draft hood, 3' single wall connector, 2 45 elbows, no horizontal runs. Both the furnace and water heater vent through 4" single wall pipe to a 6x5x4 sheet metal wye. The 5" outlet has a 4" reducer that connects to the furnace. The 6" end of the wye then connects to a 6" b vent that travels straight up, no offsets, through a wall chase and through the roof where it terminates, approximately 17'. This is the height to the tallest appliance, the water heater. Approximately 14' of actual 6" b-vent. From all the sizing guidelines I have read, it looks like I should be running a 4" b-vent connector from the furnace and can use a 4" double wall for the common vent up through the roof. I currently have 6" b-vent for my common vent. Will this cause problems with condensation and furnace efficiency? If I'm going to fix it I want to do it right! Thanks for any insite!