HEPA stands for High-Efficiency Particulate Air filter. Based on single filtration efficiency, standard HEPA filters can filter particles as small as 0.3 microns from the air, achieving a filtration rate of at least 99.97%. They are widely used in environments with strict air quality requirements such as hospitals, laboratories, and precision instrument manufacturing workshops.
Single filtration efficiency refers to the filtration capacity of the filter determined by comparing the change in the number of air particles during the single process from air intake to the discharge of clean air.
HEPA Filter Grades
According to the EU EN1882 standard, we classify HEPA filters into five grades based on their filtration efficiency: coarse filters, medium efficiency filters, sub-high efficiency filters, HEPA high-efficiency filters, and ultra-high-efficiency filters. Filters that achieve an efficiency of over 99.9% for particles of 0.3μm size are referred to as H12.
The national standard requires that HEPA materials have a filtration efficiency of F9 or above. However, as the grade increases, the purification ability becomes stronger, but the air resistance also increases. Therefore, under the same conditions, air purifiers with higher HEPA grades may actually have lower CADR values.
Why Is There a Sour Smell?
This is actually a common issue present in most air purifiers with filters. When in operation, air purifiers adsorb particles and microorganisms from the air onto the filter. Under suitable temperature and humidity conditions, bacteria can grow on the filter, producing an unpleasant odor. Additionally, activated carbon filters in air purifiers can also develop a sour smell when damp.
To address this situation, the editor from Shiyang Electromechanical recommends taking the filter out and placing it in a sunny, well-ventilated area to air dry; the "sour smell" may fade. If there is no effect, we suggest directly replacing the filter.
Why Can't HEPA Filters Be Washed with Water?
Replacing the filter is the most straightforward solution, but some friends are concerned that the cost of replacing a single filter is too high. Indeed, the price of HEPA filters for air purifiers ranges from 200 to 1000 yuan. Various materials can be used to make HEPA filters, such as PP (polypropylene) high-efficiency filter paper, PET filter paper, composite high-efficiency filter paper made from PP and PET, and fiberglass high-efficiency filter paper. Among them, PP (polypropylene) is paper-based, which typically cannot be washed with water. Another part of HEPA filters uses PET or PTFE materials, which is why many claims online suggest that HEPA filters can be washed with water. However, filters of this type have very low efficiency and are not recommended for use.