S U F S E R V I C E H A N D B O O K
I N S T A L L A T I O N
MAKE-UP AIR
Horizontal Ducts
When the heater is installed in an interior room with no roof access for vertical ducts, horizontal make-up ducts should be installed. When using horizontal ducts, two openings are required — within 12 inches (30 cm) of the top of the enclosure and one within 12 inches (30 cm) of the bottom of the enclosure. Each opening shall have a free area of not less than 1 square inch per 2000 BTUH of the total input of all appliances within the enclosure.
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 spillage, flame roll out, improper combustion, inconsistent pilot operation, and/or erratic heater shutdown.
A possible solution to this situation would be to use a SUF 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.
State Water Heaters | 11 | Technical Training Department |
Ashland City, Tennessee © 2004 | STC-077 |
