Re: Flue Pipe Insulation
A 100,000-BTUH furnace burning for one hour will generate a gallon of water in the form of vapor in the flue gas. The vent, through proper design and sizing, must keep the moisture in the vapor state until it exits the vent. This is one reason why the B vent sizing is so important!
Condensation will form in the coldest part of the vent (near the termination) when the flue gas cools to its dew point temperature. This is the temperature at which the flue gas, with its heavy load of moisture in the form of water vapor, starts to condense on the cooler walls of the vent.
The coldest run will be near termination in the attic.
Aside from adding insulation …. has anything else changed ?
Any changes to the combustion equipment ?
Have you increased the openings for attic ventilation?
The B vent sections from the attic to outside need to be a double walled insulated B vent .
Other causes can come from short cycling of the combustion equipment. The combustion equipment doesn’t run long enough to maintain warm enough temperatures in the flue pipe …. which will create condensation.
Just some thoughts.
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