Hearth & Home Technologies CL36D User Manual

12538 Rev D

02-02

CL36D AND CR36D INSTALLATION INSTRUCTIONS

Figure 27 - 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 27.

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.