Harman SF250 Coal Stove Installation & Operating Manual page 8

Possible causes of insufficient draft;
A. Chimney Leaks - Air leaking in around a loose fitting
cleanout door, flue pipe joints and/or seams not secured,
improper plug openings or defective masonry.
B. Chimney Too Short - The general rule for chimneys; 16
feet tall, three feet above the roof exit, and two feet taller
than anything within ten feet.
C. Blocked Chimney - Have the chimney cleaned and
inspected prior to installation and before each heating
season.
D. Trees Or Other Topographical Barriers - Impeding on the
chimney's operation or causing a down draft situation. This
can also be caused by adjacent buildings or another roof
of the same structure giving air currents a downward swirl.
NOTE: The chimney on the illustrated house is too low, it
should be raised to compensate for down draft potential.
E. Chimney Size - The chimney can not be smaller than the
flue exit from the appliance. Too large of a chimney could
stay too cool to promote adequate draft.
F. Chimney Offsets - Offset chimneys should be avoided.
The offset area can collect debris and cause a blockage.
G. Elbow restrictions - There should be no more than two
90° elbows or the equivalent used in connecting the stove
to the chimney flue.
H. Shared Flue - No more than one appliance shall vent into
a single flue.
8
ChImNEY & vENTINg
The most common cause of poor draft is an improperly sized
flue liner. It is recommended that the inside dimensions of
the liner be at least as large as the appliance flue outlet
and no larger than 125% of the collar for a round flue. An
example, a 8" flue collar is 50 square inches. Increased
by 25% would be 63 square inches, or approximately a 9"
round flue. In general for round liners, it is recommended
that they not be increased by more than one inch from that
of the stove collar. This will help ensure proper draft with the
lower flue temperatures.
REMEMBER; A solid fuel burning stove can only perform
as well as its venting system will allow it to.
THE MOST IMPORTANT THING TO REMEMBER ABOUT
CHIMNEYS IS THEIR NEED FOR MAINTENANCE
AND CLEANING. IF A CHIMNEY IS NOT CLEANED ON
A FREQUENT BASIS, IT WILL AFFECT THE DRAFT
AS WELL AS BEING A CONTRIBUTING CAUSE TO A
POSSIBLE CHIMNEY FIRE.
IF YOu hAvE A ChImNEY FIrE:
Wind direction
1. GET EVERYONE OUT OF THE HOUSE.
2. CALL THE FIRE DEPARTMENT.
3. CLOSE THE DRAFT CONTROL KNOBS ON THE
DO NOT USE THE CHIMNEY UNTIL IT HAS BEEN
THOROUGHLY CLEANED AND INSPECTED BY A
QUALIFIED PERSON.
STOVE.
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