Probably best bet before some bats or birds decide to nest in it are you
sure it is not used? Where did he vent the gas furnace?

Wayne

"mike" wrote in message
oups.com...
Last spring we changed over from an oil furnace to high efficiency
natural gas. The contractor who did the job put a metal cap over the
opening where the oil furnace chimney entered the masonry exterior
chimney and it is now completely unused. The top of the chimney is
still open; should it also be sealed close?