It has been my assumption that double wall vent pipe is just two metal walls with only air between. Is there or has there been in the past, anything intentionally put  between those walls besides air?

Bill,
You can look up your answer here;



Stainless on inside -- black pipe on outside -- air between

Thanks HR for the reply. This mostly confirms my belief. My concern arises from "asbestos" concerns. I have double wall vents on my gas furnace and also my water heater and one unused vent where I removed an oven. I want to be ready in case they tell me there is asbestos in there also.

Type A vents are insulated wall vents pipe(typically not asbestos), Type B are double wall air insulated. Type B is the most common vent pipe for 80% furnaces and water heaters in buildings without a chimney. Single wall is used on 80% unit in buildings with chimneys.

The type of vent pipe that the woodstove website shows is specific for woodstoves and not used for gas fired heating equipment, the construction is very similar but the materials used are different, due to the different flue gas temperatures of the material being burnt.

OK thanks Swiley it is obvious I have type B

Just a little info....Fireplace Chimney Pipe is often referred to as "Triple Wall" and must be used per code at any interior wall or ceiling locations/contact with special adaptors going up through an attic and up on a roof.