A. O. Smith Water Products Company Service Handbook
Irving, Texas 2000
©
Training Department
9
INSUFFICIENT MAKE-UP AIR
BACKDRAFT
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 air requirements. This may
result in air being backdrafted by the restaurant exhaust equipment through the heater causing flue gas spill-
age, flame roll out, improper combustion, inconsistent pilot operation, and/or erratic heater shutdown.
A possible solution to this situation would be to use a BTH with direct venting.
A less common service issue associated with a backdraft or negative pressure room would be the opening or
closing of air pressure switches. This may result in erratic or no heater operation.
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