Your air ducts are susceptible to temperature influences from the external environment. Air duct insulation separates the air within the ducts from the air outside them to minimize such effects. However, the separation is only possible if the insulation material is thick enough. Below are some of the factors that determine adequate insulation thickness.
The local weather determines the effect of the external environment on the air inside the ducts. This is because the local weather determines the ambient air temperature and humidity. Extreme temperatures call for more insulation. For example, if your area is extremely hot, you need to increase the insulation thickness to prevent the high temperatures from heating up the cold air inside the ducts.
High humidity also calls for more insulation. Otherwise, the moist air might condense and shed its water on the outer surface of the ducts. Exposure to condensation can cause corrosion if your air ducts are made of metal. Corrosion can lead to air duct damage.
The nature of the insulation material also determines how thick it should be. Different materials have different insulative capacities. Industry experts refer to the insulation capacity of materials as their R-values, which is strictly a measure of how the material prevents heat transfer.
A material with a high R-value insulates better than a material with a low R-value. Thus, a low R-value calls for more insulation thickness than a high R-value.
The duct material also determines how much heat transfer takes place between the air in the ducts and the air outside the ducts. Materials with high R-values (that allow minimal heat transfer) require less insulation than materials with low R-values.
Common examples of air duct materials include metal (steel and aluminum are common), fiberglass, fabric, and PVC (plastic). For example, metal has a lower R-value than fiberglass, so metal air ducts require more insulation than fiberglass air ducts.
Lastly, the size (length and diameter/width) also determines the necessary insulation. The effect is there because the size of the air ducts determines the volume of the air they carry. More air means more risk of heat loss, hence thicker insulation. Large air ducts also mean large surface areas, which also increases the risk of external temperature influence.
These calculations need to be precise. Otherwise, the work will be futile. Luckily, heating and cooling technicians have the knowledge and experience for proper air duct insulation.
For more information on proper air duct insulation visit a site like http://www.coeheatcool.com.