Takagi 110U Indoor (T-KJr2U-IN) Installation Manual And Owner's Manual page 8

Installation and service must be performed by a qualified installer (for
example, a licensed plumber or gas fitter), otherwise the warranty will be
void.
WARNING
The installer (licensed professional) is responsible for the correct installation
of the water heater and for compliance with all national, state / provincial,
and local codes.
The manufacturer does not recommend installing the water heater in a pit or
location where gas and water can accumulate.
The manufacturer does not recommend installing the water heater in an attic
due to safety issues
The warranty will not cover damage caused by water quality.
CAUTION
The manufacturer recommends using the direct-vent kit when the water
heater is installed in a beauty salon
manufacturer does not recommend installing the unit on a wall adjacent to a
bedroom, or a room that is intended for quiet study or meditation, etc
INCLUDED ACCESSORIES
the