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When a vent is less than 10 feet high, the vent should be at least as large as the flue collar outlet.b) Vents for draft hoods or flue collars 12 inches in diameter or less should NOT be reduced more than one pipe size.
When two direct vent water heaters are installed in a closet and the. installation situation requires the vent terminals to be vertically aligned, then. the clearances between the vent terminals must be a minimum of 9â for the. 50 gallon model and 12â for the 65 and 75 gallon models. Refer to figure 2.