I have an 80% efficient furnace. the combustion chamber is fan assisted and goes into my chimney the chimney is lined with a flexable aluminium duct. is is capped on the top.
at the point the duct goes into the chimney there is moisture. the furnace starts the fan before firing and runs after firing , but I still have a moisture problem. is there anything that can be done to keep this from happening?
I have not noticed this until recently. the furnace has been installed for 5 years.