Gas and Oil Home Heating Furnaces - is it necessary to "sleeve" your chimney after installing a 90+% efficient furnace?

I had a 94% furnace installed earlier this year. It has an enclosed combustion chamber that draws outside air for combustion and, of course, exhausts back outside. Both of these pipes are pvc, and are located on the side of my house. The only thing that uses the chimney now is my water heater.

Other people in my area have had their furnaces replaced too. In addition to the new pipes for comb. air and exhaust, they also have a galvanized metal sleeve installed in their chimney.

Did my installer skip a step by not sleeving the chimney, or is this sleeve not really necessary?

Thanks in advance, and Happy Thanksgiving.

Bob2246

a water heater with a standing pilot is ok to vent into an unlined chimney