Bosch has recently approved the ESHCK Concentric Vent Kit for the Bosch AquaStar 2700ES, 2400ES and 715ES tankless water heaters.
The ESHCK side wall concentric vent kit is actually a shell piece of stainless steel venting that will work with vent pipe manufactured by Z-Flex, ProTech Industries or Heat-Fab. (Of course, we always recommend using Z-Flex stainless steel AL29-4C vent pipe.)
Part number ESHCK is a 5" diameter shell through which you can stick a 3" x 3' piece of stainless steel vent pipe. This piece of straight pipe is terminated by either a Termination Tee or a Termination Elbow. The ESHCK shell that fits around this straight pipe creates the air intake vent pipe.
The air intake from the Bosch 2700ES, 2400ES or 715ES tankless water heater can be run using PVC and connects directly to the ESHCK. The air intake port on the ESHCK can be rotated 360 degrees around the ESHCK to bring the combustion air in from any angle. Bosch recommends that you bring the air in from the top, particularly in areas that are prone to freezing.
The ESHCK is actually 20" long, but when you stick the 3" x 3' pipe and the termination piece through the ESHCK then the total length of the ESHCK Vent Kit is about 41" long. When you add the required 3" x 90 degree elbow the total length is about 47" long. The square flashing that rests against the outside wall is 8" square.
Bosch requires that the termination tee or termination elbow be a full 12" away from your exterior wall. This is meant to ensure that the exhaust air does not get recylcled back through the air intake. Don't go beyone the 12" either as this may increase your potential for condensation in the exposed pipe section.
We sell a complete kit called the ESHCK-FULL-KIT Concentric Vent Kit that includes the ESHCK shell, a 3" x 90 degree elbow, a 3" x 3' stick of pipe and a termination tee.
Please note that this concentric vent kit will protrude quite a bit through the inside wall making it very difficult for you to mount the tankless water heater on the same wall that you are venting out of. The easiest way to use this ESHCK concentric vent kit is to mount your tankless water heater on a wall that is perpendicular from the wall that you are venting out of.
With this configuration, you will need a 90 degree elbow coming off of your water heater. Then we recommend using a horizontal drain pipe to catch any condensate that gets generated. Then you may need additoinal straight pipe to connect up to the ESHCK concentric vent kit which protrudes from the wall.
If you do want to do and "up and out" venting through the same wall you mount the heater on with the ESHCK then you will need to install your 2700ES or 2400ES tankless water heater out away from the wall. This will help you avoid using an excessive number of 90 degree elbows.
One of the big advantages of using the ESHCK concentric vent kit is that you only have to have a single hole through your exterior wall. This may greatly reduce your installation costs if you have a difficult wall to drill through, such as a thick stone wall.
Another advantage of using the concentric vent kit is that for some installations it is impossible to meet the 3' distance requirement between the exhaust and the air intake.
Aesthetically it may also be more desireable to have a single vent through your outside wall.
Please see the Bosch 2700ES Installation Manual or the 2400ES Installation Manual for the full details of installing the ESHCK Concentric Vent Kit.