There are three venting options for the Bosch 2700ES and Bosch 2400ES tankless water heaters.
AQ3ES Horizontal Vent Kit has all of the parts needed (based on the assumption that you are venting out of the same wall you have mounted the heater on).
In addition to the 90 degree elbow, wall thimble, and the intake/exhaust termination boxes, this Z-Flex 3" stainless steel vent kit comes with enough vent pipe to meet the minimum three feet requirement. The Bosch warranty requires that all exhaust systems have at least three feet of straight vent pipe.
ES VVT Vertical Vent Kit has all of the parts needed to vent up through the roof (except for the straight pipe). You will need enough straight pipe to get you three feet above your roofline.
The ES VVT Vent Kit comes with flashing, storm collar and rain cap for the roof line as well as a fire stop support, a stick of pipe, a 90 degree elbow, a vertical drain tee and a drain tube kit.
AQOK Outdoor Vent Kit turns the Bosch 2700ES/2400ES heaters into Outdoor Tankless Water Heaters. The AQOK Vent Kit bolts right on top of the heater to properly channel the makeup (combustion) air and the exhaust. The AQOK also prevents rain from getting into the tankless water heater.
With three venting options, the Bosch AquaStar 2700ES and Bosch AquaStar 2400ES heaters have the most versatility on the market!