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12-01 25 34922 Rev B
T4800 INSTALLATION INSTRUCTIONS
Figure 26 - Flue Draft
Flue draft is measured as negative pressure in the
chimney. The amount of negative pressure
determines how strong the draft is. The draft is
important because it draws the combustion air into
the fireplace and pulls the smoke out of the chimney.
There are three basic criteria essential in establishing
and maintaining flue draft:
· Availability of combustion air.
· Heat generated from the fire.
· Diameter and height of the flue system.
These three factors work together as a system to
create the flue draft. Increasing or decreasing any one
of them will affect the other two and thus change the
amount of draft in the entire system. See Figure 24.
If the fire is hard to start and smoke spills out of the
fireplace, or you find it difficult to establish and
maintain a moderately high burn rate, then the flue
draft is too low and corrective measures must be
taken.
Be sure you have air available for combustion and
that your firewood is dry and well seasoned. Build your
fires properly and according to the instructions given
in operating instructions, Starting a Fire. Be sure your
flue system is installed correctly and that it is the
proper diameter and height. Check for the following:
· All chimney sections are properly installed
and the joints are tightly sealed.
· The chimney is clean and free of creosote
buildup.
· Make sure overhanging trees and branches
are cut back within ten feet of the top of the
chimney.
· Ensure the chimney cap is clean and free of
any buildup of soot or creosote.
If you still suspect you have a low draft problem it may
be necessary to increase the volume of air in your
flue system. Since the diameter of your flue system
is matched with the size of the flue collar and should
not be changed, then the height of the system must
be increased. Add chimney sections a little at a time
until the draft improves.
In some cases, regardless of what you do, it can still
be difficult to establish the proper flue draft. This is
especially evident when using an exterior factory-built
chimney or exterior masonry chimney. Try placing
several sheets of crumpled paper on top of your
kindling as close to the flue outlet of the fireplace as
possible. Light this paper first then the paper under
the kindling. The heat generated from the rapidly
burning paper on top of the kindling should help get
the draft established.
Still other factors can affect how well your flue system
performs. Neighboring structures, high winds, tall
trees, even hillsides can affect air currents around the
chimney. Well designed chimney caps are available
that can help. Your fireplace dealer is the local expert
in your area. He can usually make suggestions or
discover problems that can be easily corrected
allowing your fireplace to operate correctly as it has
been designed, providing safe and economical heat
for your home.