Trane Gas Unit Heaters カタログ

UH-PRC002-EN

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Mechanical venting occurs when a power blower provides a positive air flow to exhaust vent gas. 
The blower may be mounted at the unit heater or at the point of termination. With a factory-
installed power venter, a pressure switch detects the flow of vent gas before the gas valve is 
allowed to open. With third party drafters, a centrifugal switch usually monitors the operation of 
the blower motor. When properly installed, the switch senses motor rotation and allows the gas 
valve to operate. Interlocking the blower to the gas valve provides some control over the 
combustion process. Using a factory unit with a pressure sensitive switch ensures that control.

With all their advantages, power venters bring some requirements as well. Each manufacturer 
determines the maximum length of pipe and fittings that his system can use for safe operation. 
Remember to count the fittings and allow for their higher resistance to flow. The total length of run 
includes not only the piping length, but the resistance of all the fittings including the termination 
cap.

Many contractors have become accustomed to using B vent with natural draft units. Used with 
power vented appliances indoors, B vent is unacceptable. B vent does not allow positive pressure 
in the vent piping to be sealed from the heated space. Proper installation uses 24-gauge, single wall 
vent pipe and each joint sealed with temperature resistant sealant or tape.

Contractors must also be aware of the conditions at the point of termination. The National Fuel Gas 
Code NFPA 54/ANSI Z223.1-1992 mandates that vent system should terminate at least 4 feet below, 
4 feet horizontally or 1 foot above any window, door, or gravity inlet to a building. Termination with 
a vent cap approved by the manufacturer should occur well above the snow line.