Understanding Your HVAC Duct in Homes
Understanding HVAC Ductwork as it applies to residential use, is a pretty straightforward process. There are generally 2-3 different types of duct you will find in homes and the concept of how it works is relatively the same across all types. This post will help you identify the type of HVAC Duct in your home, as well as understand the job of your home hvac ducts.
What Does HVAC Duct Do?
In homes with a central heating or cooling system, the duct can be viewed as the highway the fresh air, or conditioned air takes, as it makes it way into each of the areas of your home, and back to your central HVAC unit.
All Central HVAC Systems use two main duct runs to move that air:
- Supply Duct - which supplies the conditioned air throughout your home. You can identify with the supply line easiest by going to one of the vents in your floor, wall or ceiling. The air got there through one of the supply ducts. If your unit is in the attic or crawl space of your home, you can immediately recognize the supply duct as it will (should) all be wrapped in insulation.
- Return Duct - which takes air from your home, and returns it to the central unit to be conditioned. To understand the business end of the return duct, just go to the filter grill where you change your HVAC filters every month. The air entering through the filter is the return air. In your attic or crawl space, the return duct may be insulated as well, but in most cases, it is just sheet metal or flex duct.
Types of HVAC Duct in Residential Use
In most homes you will only find a few types of duct.
Sheet Metal Duct - which is a smooth wall galvanized sheet metal, either squared or rounded. Sheet metal duct work moves the air most efficiently through your home, since the inside of the duct is smooth and has no ridges or obstructions to disrupt the flow of air. in addition tot he duct itself, sheet metal duct must be wrapped with insulation before or after it is installed, in order to provide a thermal barrier between the unconditioned space and the air moving through the duct.
Insulated Flexible Duct - Likely the most common over the last 20 years or more, flex duct does exactly what it sounds like, it flexes, making it the quickest to install and easiest to use in most installations. Flex duct generally comes in compressed rolls of 25 feet, in many various sizes and varying r-values, or Insulating values.
Insulated Duct Board - This type of duct has become more popular in the past few years. The easiest way to understand duct board, it to think of a 4x8 sheet of insulated board, 1/2 - 1 inch thick. The board is then cut and squared, to form a box through which the air flows. Many new construction homes have gone to this type of duct due to the ease of installation and high performance insulating value.
In a future post, I am going to get into the duct sizing methodology, and help you understand how different sized ducts can effect your home HVAC system.