PVC pipe is a useful and versatile construction product. PVC is lighter than cast iron, cheaper than copper, and can be quickly and easily cut and glued together for virtually foolproof installation. In the construction trades, each material has its unique set of benefits that make it most suited for a particular application. While one material can conceivably be used for other purposes, factors such as available size, weight, and cost make it unlikely that PVC pipe can be used for heating and cooling ducts.
The first limitations to consider when using PVC for duct work are the available sizes of the two materials. PVC is used for exhaust vents because it can handle the volume of forced exhaust, and the exhaust typically travels a direct route over short distances. An HVAC system for a home carries much larger quantities of air, and is piped from the basement throughout the home. Therefore the size of typical PVC is not suited for the task. If the air pushed through a large aluminum duct is pushed though the smaller diameter PVC pipe, the air velocity would increase, and it would come out of the heat duct like air from a hot air hair dryer.
The second factor to consider is the weight of the product. Ducts are made from stamped, thin mill steel. This product is light weight, and is manufactured in a variety of shapes and sizes. If PVC were manufactured in the same sizes, it would weigh much more, which would complicate the installation process. For example, six-inch round PVC pipe weighs 3.53 lbs per foot, while the same size spiral metal duct is only 1.5 lbs per foot.
The third factor to consider is the material cost. While the two materials will serve the same purpose, when building a house, the difference in the material costs can become a significant barrier to cross-application. PVC and galvanized steel duct work are priced similarly. The two products are within 5 percent of each other at major retailers. Therefore for small jobs, price differential is not a huge obstacle. However, on a large job such as a new home or apartment building, the price may create a larger impediment to cross-application.
PVC pipe will carry air from one location to another. PVC is simple to install and, like steel duct work, it is durable. However, the differences in the available shapes, sizes and the products weights create significant barriers to cross application. These two products cannot and should not be substituted for each other on any large scale. In an emergency, however, or for a limited application, PVC pipe can be used for duct work.