An alternative to large ducts to carry the needed air to heat or cool an area is the use of remote fan coils or split systems. A drawback is the installation cost, which might be slightly higher than traditional Heating system. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. For the last 20–30 years, manufacturers of Heating & Cooling equipment have been making an effort to make the systems they manufacture more efficient. Building Services is part of a sector that has over 51,000 businesses and employs over 500,000 people.

Ventilating is the process of “changing” or replacing air in any space to control temperature or remove moisture, odors, smoke, heat, dust and airborne bacteria. They are often employed in basements which have a higher relative humidity because of their lower temperature (and propensity for damp floors and walls). If the ducting for the fans traverse unheated space (e. g. Central, ‘all-air’ air conditioning systems are often installed in modern residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required.

However, in humid climates much energy is required to remove excess moisture from ventilation air. Air conditioning and refrigeration are provided through the removal of heat. A metering device acts as a restriction in the system at the evaporator to ensure that the heat being absorbed by the system is absorbed at the proper rate. Today forced air systems can double for air conditioning and are more popular.