What is "Air Flush"?


With the recent higher awareness for the rapid spread of viruses and contaminants in the air, people are becoming increasingly more concerned about indoor air quality. Because of this, the term “Air Flush” is something we hear more frequently than in the past.


Air flush is the process of increasing outside air ventilation for a period of time to replace indoor air with fresh air to improve overall quality. Per code, there is a minimum amount of outside air that is required to be brought into a building, and in certain areas like restrooms and janitor closets, there is a certain amount of exhaust that is needed. To achieve an air flush, the HVAC system can bump up the outside air to exceed what it normally provides. Sizing the equipment is necessary for the system to be able to handle an increased air flush. In new buildings, the system can be sized to bring in more outside air. In older buildings, a refurbishment of the equipment, such as a louver or coil replacement, is often needed so that the system has the capacity to bring in more outside air.


Most of the time, a building's HVAC system's outside air intake capacity is running at a code minimum level. Most units are capable of handling more outside air than the code minimum. "For example," says Michael Peterson, Senior Mechanical Designer, "The system can be programmed to bring in 25% outside air rather than 15%. Modifying the sequence of operations on the controls side can allow the user to program the system to, in the middle of the night, when it’s 85 degrees, open up the system and allow fresh air to flush in for two hours. This can be done automatically through the building management system."


Air flush is beneficial for multiple reasons. First, air flush can help remove any viruses or illnesses being circulated around, and in high occupancy buildings like schools, there is an increased amount of CO2 that is being breathed in and out by the occupants. An excessive amount of CO2 can cause various negative health effects such as headaches, dizziness, tiredness, difficulty breathing, and difficulty focusing. It is important that measures are taken to ensure sufficient air quality to mitigate any viruses or contaminants that are easily spread through the air. The quality of the air we breathe must continue to be a top priority in any building in which we live, work, and play.