Installation instructions
3.4Combustion air requirements
Warning: In areas where outside temperatures routinely come close to freezing, sealed combustion operation is required. Use twin pipe or concentric terminations for combustion air and exhaust, which must be installed on the same wall or roof surface, however never facing the direction of prevailing winds. Failure to do so may result in heat exchanger freezing up and bursting. This failure is not covered under the manufacturer's warranty.
Warning: When installed in an environment where corrosive chemicals or dirty air (e.g. hair salons, car washes) are present the twin pipe system is required.
Twin pipe and Concentric pipe
The water heater is designed as a sealed combustion appliance. It is recommended that the combustion air be provided from the outside by a dedicated pipe (twin pipe) or by connecting to the concentric vent kit (see Fig. 8, 9 & 10). The combustion air pipe may be PVC or any other rigid sealed 3" or 4" pipe. Horizontal sections of the combustion air pipe must pitch down towards termination 1/4" per foot to prevent rain water from entering the appliance. When using the twin pipe method, combustion air inlet, whether terminating vertically or horizontally, must be located in such a manner as to provide a minimum 3 foot clearance from the exhaust vent terminator. See Fig. 11 and Fig. 12 Letter I, page 12.
For the maximum length of the combustion air inlet pipe, see table 6.
Warning: Vent terminations must prevent rain from entering the combustion air and exhaust vent piping.
Single pipe
Note: This appliance requires 9950 cubic feet of available combustion air, or a minimum of 1243 square feet of space with an 8 foot ceiling to operate. If the large amount of air space, which equates to about half of most average sized homes, is not available, the appliance must pull air from outside (see twin pipe system above).
Although it is permissible to draw combustion air from inside the structure, it is not the manufacturer’s recommended installation method. Always install a 3 inch elbow on the top of the combustion air inlet adaptor to prevent foreign objects from falling into the unit.
If a single pipe installation is utilized, follow guidelines
below for providing adequate combustion air for the water heater as well as any other appliances that may consume air in the space. Always follow local codes if they are more stringent.
When all requirements are followed, the unit will operate properly and safely. However, there may still be a risk of freezing due to negative draft if the other combustion appliances in the building are not supplied with sufficient combustion air. A wood stove or furnace can pull its combustion air from the heater's vent pipe, allowing the cold incoming air to freeze the cold water in the heat exchanger. Supplying more combustion air for all combustion appliances is the solution. A HVAC specialist should be consulted to design solutions for providing more combustion air. Observe the following guidelines:
Installations in structures that have been tightly constructed (air infiltration rate of 0.40 ACH or less) must be provided with combustion air per the National Fuel Gas Code. Consult a HVAC specialist if your air infiltration rate is questionable.
The space must have two permanent openings, one commencing within 12 inches of the top and one commencing within 12 inches of the bottom of the enclosure.
Each opening must have a minimum free area of one square inch per:
•1000 Btu/hr if all air is taken from inside the building
•2000 Btu/hr if all air is taken from the outside by horizontal ducts
•4000 Btu/hr if all air is taken from the outside by direct openings or vertical ducts.
Or the space must be provided with one permanent opening or duct that is within 12 inches of the ceiling of the enclosure.
This opening must have a minimum free area of one square inch per:
•3000 Btu/hr if all air is taken from the outside by a direct opening or vertical duct.
Louvers, grills and screens have a blocking effect. If the effective free area is not known, increase the sizes of your openings by 300% if your louvers are wood and by 43% if your louvers are metal. Refer to the National Fuel Gas Code for complete information.
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