Final resistance of air filter

- Sep 13, 2018 -

Dust accumulates with the filter, resistance increases, when resistance increase to a certain value´╝î the filter is scrapped and need s to be replaced. The resistance of the new filter is called initial resistance , the resistace when the filter is scrapped need to be changed is called final resistance.

\Several factors influencing the final resistance of air filter,

  1. Mechanical strength of filter

    Large size air filter , frame and fixtures take up a small proportion. When there is too much resistance, loose or damaged filters may be caused,

    Determine the final resistance in this respect, the value is generally large, so it's not genarally considered.

  2. High efficiency filter replacement cost(price+labor)

  3. Resistance energy consumption for filter operation

  4. System air volum allowed variation range

  5. Change of filtration efficiency

Low efficiency filters (below G4) offen use coarse filters with diameter > 20m.

The fiber clearance is about 200-400m, The filtered wind speed is about 0.5-2m/s, excessive resistance , dust accumulation on the filter will be carried away by air flow again, now the resistance is not going up, but filtration fefficiency has falleb dranatucakkt, so for such filters, consider replacing them before they become less efficiency.

\According to the previous factors:

Filte efficiency specificationPA
G3(coarse filter) 
150 - 200
F5-F6 (mid efficiency) 
F7-F8(up mid efficiency)
F9-H11(sub HEPA)  



Air filter is usually the most important part of ventilation system.  For the air conditioner designers, the fan and air conditioner shall be selected according to established initial and final resistance of the filter and the allowable air flow range to select fan and air conditioner. And provide final resistance value of when need replacement.

For existing ventilation and air conditioning systems, if there is no final resistance value and equipment details provided by the air cinditioning supplier, the air volume of the system should be allowed according to its own permissible range and other conditions to determine the final resistance.