The chimney was used by both furnace and gas heater before I replaced the
furnace with 92% furnace that has now separate PVC pipe chimney through the
basement wall. The old metal chimney is used now only by gas heater. The
chimney consists of two pipes: light aluminum inner pipe and heavier metal
outer pipe. The chimney goes from the basement to the roof through vertical
square opening. The opening is larger then round chimney (outer metal pipe)
and warm air is sucked away from heated insulated basement and cold air is
sucked in to the basement from the attic. So this void space around the
chimney outside pipe must be closed somehow with insulation.


"George E. Cawthon" wrote in message
...
What is a heater chimney? you mean the chimney for a
furnace? Most metal chimneys are not zero clearance and
generally require a 3 inch clearance. You treat chimneys
just like you do sunken light fixtures (ones that protrude
above the ceiling). You build a ring of sheet metal around
the fixture to keep insulation or other material away from,
or in this, case the chimney to a height slight greater than
the depth of the insulation.

And no, you do not wrap any kind of insulation around the
chimney. There is no reason to and it would serve no
purpose (if it is a zero clearance chimney) and would be
dangerous if the chimney requires a 3 inch clearance.

Alexander Galkin wrote:

I am adding insulation to the attic that already has insulation. I have
a
heater chimney that goes through the attic. Can I use John Manville
Kraft
R-19 unfaced batts to add insulation to the attic? The package says its
for
wall/floor/crawl spaces. I assume it can be used for attic too. Can
batts
touch heater chimney? The chimney actually has two pipes, one inside
another. The inner pipe is very thin aluminum pipe while outer pipe is
regular duct metal pipe. If batts cannot touch chimney can I use
thermofiber
insulation around the chimney and keep batts 3" away from it? I think
thermofiber insulation does not burn and can touch hot objects.