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Furnaces
To raise the tank temperature and increase the BTU capacity of the tank:
➤ Place an insulated, fire-resistant blanket over the tanks.
➤ Place an illuminated 75-watt light bulb under the blanket.
➤ The temperature of the bottle should rise 10°–20° F over a brief period of time, which could double the BTU
capacity of the tank from the preheating state.
Check the Ducting
Each furnace has a specific BTU size that requires a minimum number of square inches of heat ducting to support
the airflow. The standard so-ducting size is 4" (12 sq. in.), which helps identify the minimum number of ducts
needed for any model of furnace, based on the minimum ducting for the BTU size. For example, if a furnace has a
requirement of 24 sq. in. minimum ducting, then a minimum of two ducts must be used.
➤ Determine the type of duct system:
– So duct: routed throughout cabinets or set below flooring
– Hard duct: built within flooring
➤ Use a mirror and a flashlight to inspect the duct system and identify potential issues:
Type of Duct System Potential Issue
So-Duct System
• Ducts do not meet the minimum requirements, including the minimum number
of ducts, as outlined in the installation instructions
• There are too many loose bends/elbows
• Ducts are smashed or kinked
• Ducts are torn or poorly connected
Hard-Duct System
• Ducts do not meet the minimum size requirements as outlined in the installation
instructions
• Ducts are collapsed, have holes, or exhibit other damage
• The furnace is not lined up with the designated opening in the floor
➤ Check for proper duct connections at the furnace and heat registers.
– The duct runs must be straight and taut. Excess ducting slows the airflow through the duct.
– The heat ducts must be clean and free of obstructions.
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