Air Supply - State Water Heaters SBN 71-120NE Service Handbook

SBN TANK TYPE COMMERCIAL GAS WATER HEATER

Air Supply

Stoichiometric or theoretical complete combustion requires 10 cubic feet of air per
1,000 BTUH of gas supplied. The National Fuel Gas code also recommends an
additional 2.5 cubic feet of "excess" air.
For information on minimum make-up air opening sizes for various building installations,
refer to the National Fuel Gas Code NFPA 54, ANSI Z223.1, Sec. 5.3.
Insufficient make-up air is a major cause of combustion problems.
One common example is in a restaurant installation where exhaust vent equipment was
not considered in sizing make-up requirements. This condition may result in air being
backdrafted by the restaurant exhaust equipment through the heater causing the draft
proving switch to open and/or erratic heater shutdown.
©2003
SERVICE HANDBOOK
1,000
BTU
Insufficient Make-Up Air - Backdraft
10 CU.
FT.
COMB.
AIR
2.5 CU.
FT.
EXCESS
AIR
6
Technical Training Department
Ashland City, Tennessee