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SUF SERVICE HANDBOOK
INSTALLATION
State Water Heaters Technical Training Department
Ashland City, Tennessee © 2004
9 STC-077
AIR REQUIREMENTS
MINIMUM AIR FOR COMBUSTION
10 Cubic Feet of Air Per 1000 BTUH
Stoichiometric or theoretical complete combustion requires 10 cubic feet of air per 1000 BTUH of
gas input. The National Fuel Gas Code also recommends an additional 2.5 cu.ft. of “excess air”.
This 12.5 cu.ft. minimum supply air per 1000 BTUH input applies to natural and propane gas mod-
els.
The National Fuel Code also specifies minimum make-up air opening sizes for various building
installations (Ref: NFPA 54, ANSI Z223.1, sec 5.3).
MAKE-UP AIR
Direct Vent Installation
This model is approved for direct venting either horizontally or vertically or conventional venting
horizontal or vertical. Direct venting avoids using room air for combustion and eliminates the need
for additional air intake ducts.