Heatilator C40 Owner's Manual page 18

Another appliance in
home also exhausting
air (furnace, fan,
dryer, etc.)?
Overhead fan
operating?
Doors opening
and closing?
Window closed
for start-up?
Unsealed
can lights?
Air register from
furnace near
fireplace?
Outside air
Combustion
closed?
air control
Overhanging
tree?
Bird's nest
or leaves in
termination
cap?
Structural
changes in
chimney area?
Creosote buildup
in flue?