This termination is specifically designed to work with PH28 Direct Vent models.

Sweet Installation Manual (pdf, 124KB)
All inclusive vent kit for through the wall terminations above the heater. Use this termination when the PH28DV is mounted on the same wall as vent penetration and the wall thickness is 8.25"-11.75". When the water heater is mounted to a wall other than the vent penetration use the "Bazooka" termination (see PH-28 DV Water Heater installation manual [pdf, 4.0MB] for more details).