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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22681
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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I have a condensation problem with my furnace vent pipe. I

Resolved Question:

I have a condensation problem with my furnace vent pipe.
I have a masonary chimney aprox 30' rise ,a 5" flue liner aprox 15' of horizontal pipe {slight rise} inside an unconditioned basement,{about 50 deg.} its a 75,000 btu comfortmaker furnace 2004 model year,I've slowed the fan to med lo the temp diff. across the ht.exchanger was about 50 deg. as I recall,the hot water heater is not vented to this same chimney.Since the contractor installed this furnace in 2005
condensate has leaked from the elbows or seams inside the basement aprox. 5 gals./month sometimes more depending on the amount of run time.someone suggested b-vent pipe to solve this problem,what do you think,do you have any suggestions.
Submitted: 6 years ago.
Category: HVAC
Expert:  BillyHvac replied 6 years ago.


It is because of this situation that code is in place to control this.


The unit is supposed to have a chimney liner the proper size installed in the chimney.


The flue gases are obviously condensing in the vent by lack of draft and temp. The contractor at the time was to have installed b vent and liner.


Nothing else will remedy this until the liner and b vent are in place.



Customer: replied 6 years ago.
Every time I have asked this question of an hvac tech the answer has been tha 5" flu liner is the proper size for the30' rise.
Expert:  BillyHvac replied 6 years ago.


It is not is unconditioned space.


And a 5" clay in 5" is totally different than 5" round. And at 75000 btu I doubt you have a 5" vent pipe unless older 70 % efficient.


The fact you are condensing shows the flue gas is not exiting the flue in a timely manner and is condensing due to being stalled.



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