What Is Residential HVAC Static Pressure?

Static Pressure

• The static pressure of a heating or cooling system is the amount of pressure that is present in a home's air ducts. The air that moves down the air ducts from the heating or cooling system has to overcome the static pressure so as to push the heated or cooled air into each room. Higher pressure means that the overall airflow will be lessened because the air must move past more pressure, and this can affect energy costs and heating or cooling performance. Contact a heating, ventilation and air conditioning professional for specific information about the static pressure needed for your actual system, based upon your home size, furnace or air conditioner capacity and air duct system.

System Size

• The output of a home heating or cooling system must be considered to properly heat or cool the home. Larger homes need a higher output than smaller houses and, even if the ductwork is measured and installed properly, if the heating or cooling unit is not sized appropriately, the home will not heat or cool as desired. The equalized static pressure may be affected because not enough air will be produced. Typically, the HVAC expert will calculate the cubic feet per minute of warm or cool air that each room needs prior to the purchase and installation of the heating or cooling system, depending upon the size of each room. This is then matched against the capacity of the heating/cooling unit.

Ductwork

• The furnace or air conditioner blower fan produces warm or cool air when running but there is a limit to how much air the blower can produce at any one time. This air, or energy, is further divided as the air exits the heating or cooling unit and is split into various air ducts and transferred throughout the home. In other words, the total energy produced by the blower is not the same amount of energy that reaches each room. The energy, or air, that is produced by the blower must push past the pressure in each air duct and expel the air into every room with an air register. As the duct work moves away from the primary heating or cooling system, which should be centrally located in the home for best effectiveness, the ductwork diminishes in size. The duct that exits from the heating/cooling unit is larger in size than the individual ducts that travel to each room to help keep the pressure at each register constant, with bigger ducts reaching rooms along the inside perimeter of the house and smaller ducts reaching rooms located near the center of the home. The pressure of each air register in each room must be the same to create an equalized system.

Damper Control

• Another factor in the equalized static pressure of a heating or cooling system is the damper control system. A damper control should be installed in each air duct within a home to allow individualized control over the air entering each room. The damper controls can help improve the overall pressure of the heating and cooling system by increasing or decreasing the amount of air that enters each room. Ask your HVAC expert for assistance in determining how far open or closed the damper in each room should be for the best equalized static pressure.