When do you need to change AHU filters?

When to Change Filters of Air Handling Unit

An air handling unit, is a system used to circulate and condition the air in your heating, ventilating and air conditioning unit. Check and replace air-handling unit (AHU) filters regularly to ensure proper function and maximize system operation. Keeping filters and coils clean can dramatically improve the efficiency of the entire HVAC system.

Damage of polluted filters

  • Pollutedfilters can increase the energy demand on fans.
  • Pollutedfilters can reduce the volume of supply air, resulting improper system operation.
  • Polluted filters will cause poor indoor air quality, breed bacterias, can’t meet the clean class of clean room.

After replacement, youll have following benefits:

  • Cost benefits: Energy savings result in cost savings. Regular filter replacement prevents pollutant overloading and improves energy performance.
  • Environmental benefits: Reducing energy use always has an environmental benefit. In addition, filter replacement can result in more efficient filter function and improved air quality.
  • Health and safety benefits: Regular filter replacement should improve indoor air quality, enhancing patient and staff experience.


When to Change Filters

Generally speaking, the 30% efficient prefilters(G3/G4 or MERV7/8) require to clean or change at least monthly, metal type filters can be washed for many times, non woven filters usually can only be washed for one or two times, then need to be replaced by new filters.

The 90% efficient final filters(G7/G8 or MERV 13/14) require to change every six month, at least once a year, which depends on working conditions.

Due to protection of prefilter and final filters, HEPA filter can last longer time, usually change once a year or longer time.

To know exactly when to change filters, you can use a differential-pressure gauge to check the air resistance across each filter. When the final resistance of filter is higher than twice of initial resistance, the filter should be changed. Most AHU also  installed a differential pressure gauge for bag filters or HEPA filters, an alarm function tied to a maximum pressure drop also will alert technicians to check and change the filters, but notification will occur only at maximum filter loading set point.