How long life of a Air filter

- Apr 24, 2018 -

Air filter is the core equipment of the air conditioning purification system. The filter will form resistance to the air. As the filtered dust increases, the filter resistance will increase. When the filter has too much dust and the resistance is too high, air quantity passing through the filter will be reduced, or the filter will be partially penetrated. Therefore, when the filter resistance increases to a certain value, the filter will be scrapped; therefore, use a filter to grasp the appropriate life cycle. In the absence of damaging to the filter, the service life is generally determined by resistance.


The service life of the filter depends not only on its own merits, such as filter material, filter area, structural design, initial resistance, etc., but also related to the concentration of dust in the air, the actual air volume used, the setting of the final resistance, and other factors.

To master the proper life cycle, it is necessary to understand the changes in its resistance.

1. Rated initial resistance: The initial resistance provided by the filter sample, filter characteristic curve or filter test report at rated air flow.

2. Design initial resistance: filter resistance under system design air flow (should be provided by air conditioning system designer).

3. Initial operation resistance: At the beginning of the system operation, the resistance of the filter; if there is no instrument for measuring the pressure, can only take the resistance under the designed air volume as the initial resistance of the operation (the actual running air volume cannot be exactly equal to the design air volume);

During operation, the resistance of the filter beyond the initial resistance should be regularly checked (each filter segment should be equipped with a resistance monitoring device) to determine when to replace the filter.


Filter replacement cycle, see the following table:



Replacement cycle

Fresh air inlet filter

Is the mesh more than half blocked

One week to clean


Resistance ≧60pa+rated initial resistance ,or resistance=2xDesign or operation initial resistance

1-2 months

Medium air filter

Resistance ≧80pa+rated initial resistance ,or resistance=2xDesign or operation initial resistance

2-4 months

Sub-HEPA filter

Resistance ≧100pa+rated initial resistance ,or resistance=2xDesign or operation initial resistance

More than one year

HEPA filter

Resistance ≧160pa+rated initial resistance ,or resistance=2xDesign or operation initial resistance

More than three years

Note: Low-efficiency filters generally use coarse fiber filter material, and the gap between the fibers is large. Excessive resistance may cause the dust on the filter to blow away. In this case, the filter resistance will no longer increase, but the filtration efficiency is reduced to almost zero, so the final resistance value of the rough filter must be strictly controlled!

Determining the final resistance must consider several factors. If the final resistance is set low, the service life is short, long-term replacement costs (filter costs, labor costs, and disposal costs) are correspondingly high, but operating energy consumption is low; so each filter should have the most economical final resistance value.


Final resistance recommended value:


Recommended final resistance≦ Pa

G3 prefilter




F5-F6 Medium efficiency


F7-F8 higher Medium efficiency


F9-H11 Sub-HEPA


HEPA filter


The dirtier the filter, the faster the resistance increases. Excessively high final-resistance does not mean that the service life of the filter will be prolonged. Excessive resistance will drastically reduce the air volume of the air-conditioning system. Excessive final resistance is undesirable because of the high energy consumption.

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