18-CE07D1-1C-EN
21
EXTERNAL MASONRY CHIMNEY
Venting of fan assisted appliances into external chimneys (one or more walls
exposed to outdoor temperatures), requires the chimney be lined with type "B",
double wall vent or suitable flexible chimney liner material. This applies in all
combinations of common venting as well as for fan assisted appliances vented
alone.
The following installation practices are recommended to minimize corrosion caused
by condensation of flue products in the furnace and flue gas system.
1.
Avoid an excessive number of bends.
2.
Horizontal runs should pitch upward at least 1/4" per foot.
3.
Horizontal runs should be as short as possible.
4.
All vent pipe or connectors should be securely supported and must be inserted
into, but not beyond the inside wall at the chimney vent.
5.
When vent connections must pass through walls or partitions of combustible
material, a thimble must be used and installed according to local codes.
6.
Vent pipe through the roof should be extended to a height determined by
National Fuel Gas Code or local codes. It should be capped properly to prevent
rain water from entering the vent. Roof exit should be waterproofed.
7.
Use type "B" double wall vent when vent pipe is routed through cool spaces
(below 60° F.).
8.
Where long periods of airflow are desired for comfort, use long fan cycles
instead of continuous airflow.
9.
Apply other good venting practices as stated in the venting section of the
National Fuel Gas Code ANSI Z223.1 "latest edition".
10.
Vent connectors serving appliance vented by natural draft or non-
positive pressure shall not be connected into any portion of a
mechanized draft system operating under positive pressure.
11. Horizontal pipe runs must be supported by hangers, straps or other suitable
material in intervals at a minimum of every 3 feet of pipe.
12. A furnace shall not be connected to a chimney or flue serving a separate
appliance designed to burn solid fuel.
13. The flow area of the largest section of vertical vent or chimney shall not exceed
7 times the smallest listed appliance categorized vent area, flue collar area, or
draft hood outlet area unless designed in accordance with approved
engineering methods.
Maximum Vent or Tile Lined Chimney Flow Area = [
π
π
(D*)
2
]/4 X 7
* Drafthood outlet diameter, flue collar diameter, or listed appliance categorized
vent diameter.
Gas Vent Termination
Roof Pitch
Minimum Height
Flat to 6/12
Over 6/12 to 7/12
Over 7/12 to 8/12
Over 8/12 to 9/12
Over 9/12 to 10/12
Over 10/12 to 11/12
Over 11/12 to 12/12
Over 12/12 to 14/12
Over 14/12 to 16/12
Over 16/12 to 18/12
Over 18/12 to 20/12
Over 20/12 to 22/12
1.0 Feet
(a)
1.25 Feet
1.5 Feet
2.0 Feet
2.5 Feet
3.25 Feet
4.0 Feet
5.0 Feet
6.0 Feet
7.0 Feet
7.5 Feet
8.0 Feet
(a)
This requirement covers most installations
Vertical Wall
Lowest Discharge
Opening
8 ft.
Listed
Cap
Minimum
Height
Roof Pitch is X/12
The vent termination should not be
less than 8 ft. from a vertical wall.
(a)
This requirement covers most installations
