The interior mount version of the revolutionary V53e.  Note:  Requires vent kit.  Call for vent pricing (depends on project, local codes, etc).  Great for environments where it gets very cold outside because you do not have to worry about your unit freezing up on the exterior wall.  5.3 gallons per minute.

Note, these machines can easily be linked into manifold-style systems that modulate each other.  Please call for details if you need multi-unit solutions for heating water.