HVAC Maintenance: Static Pressure Regulation is Key to HVAC Efficiency

One of the tasks completed during a preventative maintenance visit is a static pressure check of the air flowing from the supply vents. A technician uses a manometer to measure the difference in pressure between two points in a system, in this case, between the air pressure inside the vent and outside the vent. This test measures the airflow pressure generated by the HVAC blower motor, determining the output function necessary for conditioning air.

When air conditioner airflow is reduced, the results will be uncomfortable for occupants and disastrous for components of the system. It can cause ice to build up on the refrigerant coils and can lead to the failure of the compressor, which is an expensive failure. What causes low airflow in supply vents?

A Clogged Air Filter. The value of air filters cannot be exaggerated. Filters scrub airborne particles from the indoor air, a vital function to keep occupants healthy and safe. Filters remove dust, pollen, and dander from the air every time a heating or cooling cycle begins. The filters are designed to be replaced regularly—about every three months is recommended. And when replacement is neglected, the filter will clog and greatly reduce the airflow.

Blocked Vents and Plenums. When the blower motor is pushing air through the ductwork, it is pulling air from throughout the home via several return air vents or plenums. This flow of air to and from the central air conditioner is essential for mixing and conditioning indoor air. Several return air vents will be found near the ceiling on every floor and if covered by a drape or wall hanging, they prevent air circulation. At least one supply air vent should be found in every room; occasionally these vents get covered by furniture or area rugs.

Leaking or Blocked Ductwork. A network of ducts was installed in your home during construction to accommodate the central heating and air conditioner system. The ducts should be securely sealed to adequately move air around the house. When leaks develop, the air is pushed out of the vent into unconditioned space in the walls, basement, or attic. This removes air from circulation and forcefully pulls unconditioned air from the outside. The imbalance results in dirty hot or cold air making a home unsafe and uncomfortable. Leaks can be damaged by invasive pests, accidental contact, and aging sealants.

Items that find their way into the ductwork can create a blockage or partial block of the duct and reduce air pressure. Pest and people are potential sources for items being inserted into the ducts.

Weakened Blower Motor. The blower motor is a powerful fan that moves an incredible amount of air several times per hour. A normal blower motor moves the entire volume of indoor air every two minutes, which is quite impressive. This powerhouse component works incredibly hard over the years and if this part weakens due to wear, it will reduce the static pressure in the vent. If this is a singular problem, the blower motor can be replaced: if it is one of several failures combined, it may indicate a more systemic problem.

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