State Industries STC-074 specifications Comb AIR

SBN TANK TYPE COMMERCIAL GAS WATER HEATER

SERVICE HANDBOOK

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.

1,000 BTU

10CU.

FT.

COMB.

AIR

2.5 CU.

FT.

EXCESS

AIR

Insufficient make-up air is a major cause of combustion problems.

Insufficient Make-Up Air - Backdraft

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 6 Technical Training Department

Ashland City, Tennessee