by Patti Dees
Two common HVAC questions are: what is the difference between central air and forced air, and which is better. These questions are based on a misunderstanding of the terms and how they are sometimes used. A closer look at the systems clarifies the relationship between central air and forced air.
What is central air?
Central air is a type of air conditioning unit. There are also central heating units available. With central air or heat, air from within multiple rooms passes through a centralized unit where it is cooled or heated – aka, conditioned – to meet a temperature as set on a thermostat. Once the air is conditioned, it is redistributed throughout the building.
The thermostat is linked to the centralized unit and controls the temperature for several rooms rather than each having its own. Larger buildings may have multiple units to serve specific areas, or zones, which encompass a floor or suite of rooms. In this case, each zone will have its own thermostat that ties into its specific unit.
Two basic types of central air are the split system and the packaged system. The split system divides the heat transfer components between an indoor and an outdoor unit. The indoor unit includes the evaporator while the condenser and compressor are in the outdoor portion. A packaged system contains the same components but in a single outdoor unit.
Central air units may include fans to help move the air past the individual heat transfer components. However, they are often found connected to an air handler that provides the bulk of the circulation.
What is forced air?
Forced air systems are essentially air handling systems. They move air throughout a building using ducts that connect vents in the building to the air handler. The ducts are separated into two networks, both of which link back to the air handler. Supply ducts bring air to the rooms, and return ducts send air back. Using fans and blowers, the air is forced through the ducts, hence the name. Additional fans may be placed in other parts of the network to improve functionality.
Unless it is installed solely for ventilation, a forced air system must be connected to equipment that alters the temperature of the air. Some forced air systems include heating elements or are connected to furnaces, boilers, or heat pumps. If the heat is generated from a furnace that burns fuel, the system will also need a flue to exhaust combustion byproducts.
Because of the close association between heating and forced air, the term is sometimes used to refer to the heating system as a whole. However, a forced air system can be used for moving air cooled by an AC unit, such as a central air unit, providing outdoor ventilation, or for filtering out dust and allergens to maintain indoor air quality.
Central air and forced air are different, but not in a way that one is better than another. Central air can, in fact, be combined with a forced air circulating system or a forced air heating system. By asking questions from professionals such as those at Therma and learning about a few HVAC basics, owners or building managers can ensure that their HVAC investment will meet their expectations.
Patti draws on her background as a chemical engineer to share information with readers on technology, manufacturing, and construction.
Sources and Additional Reading
Carrier – What Is Central Air and How Does It Work?
Forbes- What Is Forced Air Heating?
Innovative Building Materials- Understanding HVAC Systems: Is Central Air System Different from Forced Air System?
Sustainable Heating – Centrally Ducted Forced Air
