The recommended placement for the IAQ-I is 4-6 feet off the ground, wall mounted. The unit should be away from windows and doors for accurate sampling.
To mount the unit to the wall, first make sure an outlet is available within a distance equal to the length of the power cable from where the unit will be installed. Then place the 2 command strips at the back of the enclosure, as show on the picture below, and mount it on the wall using a level.
The number of recommended units is one per HVAC system or one per floor if that system serves multiple floors. Some contractors install an IAQ-I in a representative example of a system and assume similar IAQ metrics in systems of similar design.