HVAC For Beginners

HVAC Duct Design

Understanding the Key Principles and Best Practices

Proper hvac duct design will help to ensure a long heating and cooling system life. The effects of improper design can be very serious and expensive to correct. So, what is a properly designed hvac system? The proper system will deliver clean, fresh air (in proper proportion) to each room in the home. It will be properly sized to ensure the quietest, most efficient operation of the hvac system. The process begins with deciding on the type of hvac unit you will use. This is important to do first so that the duct system will be the proper size. For example, a heat pump system requires larger ducts than the typical furnace/air conditioner system for proper operation. Next, you must decide what materials will be used. Some systems are fabricated from a product called flexible ducts or flex for short. This is basically a reinforced plastic tube with insulation and a protective jacket on it. This is usually the easiest and least expensive to install. Another option is sheet metal. This is usually harder and therefore more expensive to install. Typically, it will last longer than a flex system. But, there can be more noise transmitted through the system. A common complaint is due to noise as the system fan starts and stops. A system made from pressed fiberglass is called ductboard. This is usually more expensive to install. The benefits are improved energy efficiency as well as quietest system operation. Sometimes a combination of these materials is used. The most common combination is to use metal ducts for the main trunk lines and flexible ducts for the branches to the individual rooms. That way you can receive all the benefits at a more friendly price. Now, the options for proper indoor air quality must be considered. This will affect the size of the hvac equipment as well as the size of the ducts. Some of the air cleaning options such as media filters and activated charcoal filters cause more resistance to air flow. This is normally accounted for by properly designing the return air system. Finally, all this information can be entered into a computer program to figure the size of the hvac unit required. This process is called a load calculation.


If a contractor offers to install a heating/cooling system without performing a load calculation, you should find a new contractor. This is a sure sign that you are not going to get a quality job. If they say that they can get it right just because of their experience, you need to run in the opposite direction. Proper design will result in money savings for you in three ways. First, if you are purchasing a new system, properly sized systems will normally be smaller and therefore less expensive. It will also operate more efficiently saving you on your monthly utility bills. Finally, a properly designed system will require fewer repairs and last longer. With proper hvac duct design, you will also have a healthier more comfortable home.