These are 2 units placed in a thight attic space, there is still easy access to the units through an attic hatch, but it still involves getting a ladder to get to them
This is a unit in a small plant room in a house in Donaghmore, it has very easy to access.
The point i am trying to make is that the easier it is to get access to the unit the more likely that basic maintenance will be done. People are more likely to check and clean the filters regularly if the unit is located in a utility, plant room or garage than if it is placed in an attic.