Thread: Flue liner for gas devices

In an old house with an unlined 7.5 x11.5 chimney, I need to know what is the proper metal flue liner size to use. There is an old gas furnace with a 4 " vent and old water heater with a 3 " vent. They both use the flue. Some contractors are saying that there must be two liners, one for each device. Another, says that one larger flue is enough. Does any one know what the normal code is?

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John,
Why do you need to know the proper vent liner size??? That's what the HVAC specialists needs to know. In any event, both the furnace and hot water heater can vent into the one flue in the chimney (at least in my area). Furthermore, if the furnace is old like you say (and has a draft diverter) then the chimney more than likely does not need a liner at all. Did you notice any corrosive deposits on the vents which sugests that the chimney isn't drafting properly or what has spurred this question on?

Bob Dalga
Home Analysts
Kalamazoo, MI

Insufficient data - fatal error.

You would need to know the Btu/hr input for all appliances and the height of the chimney (for the proper vent size from the connector up), along with the height of the connector (for the proper connector size). Also, whether either was fan assisted or not.