COMBUSTION AIR SUPPLY
All installations must comply with Section 5.3, Air for Combustion and Ventilation of the National Fuel Gas Code, ANSI Z223.1 or Sections 7.2, 7.3 or 7.4 of CAN/CGA B149.1 or .2 Installation Code - latest edi- tions.
This furnace is certified to be installed with one of three possible com- bustion air intake configurations.
1.OUTDOOR COMBUSTION AIR: This is a direct vent configuration where the combustion air is supplied through a PVC or ABS pipe that is connected to the PVC coupling attached to the furnace and is terminated in the same atmospheric zone as the vent. This type of installation is approved on all models. Refer to Figure 36.
2.AMBIENT COMBUSTION AIR: Combustion air is supplied from the area surrounding the furnace through openings in the furnace casing. The combustion air and the vent pipes are not terminated in the same atmospheric zone. Refer to Figure 21 for vent termina- tions. Refer to "Ambient Combustion Air Supply" for proper instal- lation. Refer to Figure 36.
3.VENTILATED COMBUSTION AIR: Combustion air is supplied through a PVC or ABS pipe that is connected to the PVC coupling attached to the burner box and is terminated in a ventilated attic or crawl space. The combustion air and the vent pipes are not termi- nated in the same atmospheric zone. Refer to Figure 37 for attic and crawl space termination. Only the combustion air intake may terminate in the attic. The vent must terminate outside.
Outdoor Combustion Air
Combustion Air Intake/Vent Connections
This installation requires combustion air to be brought in from outdoors. This requires a properly sized pipe (Shown in Figure 30) that will bring air in from the outdoors to the furnace combustion air intake collar on the burner box. The second pipe (Shown in Figure 30) is the furnace vent pipe.
COMBUSTION AIR | Vent pipe cements |
| into socket just |
| above top panel |
Or vent pipe may be clamped into outlet of drain coupling
FIGURE 36: Combustion Airflow Path Through The Furnace Casing
This type of installation requires that the supply air to the appli- ance(s) be of a sufficient amount to support all of the appliance(s) in the area. Operation of a mechanical exhaust, such as an exhaust fan, kitchen ventilation system, clothes dryer or fireplace may cre- ate conditions requiring special attention to avoid unsatisfactory operation of gas appliances. A venting problem or a lack of supply air will result in a hazardous condition, which can cause the appli- ance to soot and generate dangerous levels of CARBON MONOX- IDE, which can lead to serious injury, property damage and / or death.
An unconfined space is not less than 50 cu.ft (1.42 m3) per 1,000 Btu/ hr (0.2928 kW) input rating for all of the appliances installed in that area.
Connects to collar on top 
of burner box
Vent pipe cements into socket just above top panel
Or vent pipe may be clamped into outlet of drain coupling
Rooms communicating directly with the space containing the appli- ances are considered part of the unconfined space, if doors are fur- nished with openings or louvers.
A confined space is an area with less than 50 cu.ft (1.42 m3) per 1,000 Btu/hr (0.2928 kW) input rating for all of the appliances installed in that area. The following must be considered to obtain proper air for combus- tion and ventilation in confined spaces.
Combustion Air Source From Outdoors
The blocking effects of louvers, grilles and screens must be given con- sideration in calculating free area. If the free area of a specific louver or grille is not known, refer to Table 12, to estimate free area.
Table 12: Estimated Free Area
FIGURE 35: Direct Vent Air Intake Connection and Vent Connection
The combustion air intake pipe should be located either through the wall (horizontal or side vent) or through the roof (vertical vent). Care should be taken to locate side vented systems where trees or shrubs will not block or restrict supply air from entering the terminal.
Also, the terminal assembly should be located as far as possible from a swimming pool or a location where swimming pool chemicals might be stored. Be sure the terminal assembly follows the outdoor clearances listed in Section #1 “Outdoor Air Contaminants.”
Ambient Combustion Air Supply
This type installation will draw the air required for combustion from within the space surrounding the appliance and from areas or rooms adjacent to the space surrounding the appliance. This may be from within the space in a
Wood or Metal | Wood | |
Louvers or Grilles | Metal | |
|
| |
Screens+ | 1/4” (6.4 mm) | |
mesh or larger 100% | ||
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|
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* Do not use less than 1/4” (6.4 mm) mesh
+Free area of louvers and grille varies widely; the installer should follow louver or grille manufacturer’s instructions.
Dampers, Louvers and Grilles (Canada Only)
1.The free area of a supply air opening shall be calculated by sub- tracting the blockage area of all fixed louvers grilles or screens from the gross area of the opening.
2.Apertures in a fixed louver, a grille, or screen shall have no dimen- sion smaller than 1/4” (6.4 mm).
3.A manually operated damper or manually adjustable louvers are not permitted for use.
4.A automatically operated damper or automatically adjustable lou- vers shall be interlocked so that the main burner cannot operate unless either the damper or the louver is in the fully open position.
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