The Indoor Unit either directly acts as the air outlet and return air in one as is the case for split, or multi-split units, or have a series duct work in a roof space taking the air to all the rooms using usually ceiling or pelmet outlets, plus a "return air" grill and filter, hence the are called a ducted system. As a ducted system has only one indoor unit, they are usually less expensive for installations greater than two rooms.

Large Buildings often use a different air conditioning system involving a cooling tower mounted on the roof of the building, which uses water and chemicals.

· Running Costs 
With electricity costs always on the rise, choose a system with the lowest running costs. A slightly more expensive system with lower running costs will be more economic for you the years ahead.

· Spare Parts 
Obtaining spare parts in the years ahead is important. There are cheap systems available made in factories.