| Last spring we changed over from an oil furnace to high
| natural gas. The contractor who did the job put a metal cap
| opening where the oil furnace chimney entered the masonry
| chimney and it is now completely unused. The top of the chimney
| still open; should it also be sealed close?
Not "sealed" ait tight, but closed off with a fairly fine mesh or
something similar that's permanent in nature. They make covers
for that purpose. Don't seal it or you may end up with crumbling
problems with it. And, be positive nothing else vents into it on
its way to the roof!