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Filter Media Ratings |
Air filters are commonly described and rated based upon their collection efficiency, pressure drop (or airflow resistance), and particulate-holding capacity. Two filter test methods are currently used in the United States: American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 52.1-1992 ASHRAE Standard 52.2-1999
Standard 52.1-1992 measures arrestance, dust spot efficiency, and dust holding capacity. Arrestance means a filter's ability to capture a mass fraction of coarse test dust and is suited for describing low and medium-efficiency filters. Be aware that arrestance values may be high, even for low-efficiency filters, and do not adequately indicate the effectiveness of certain filters for chemical or biological protection. Dust spot efficiency measures a filter's ability to remove large particles, those that tend to soil building interiors. Dust holding capacity is a measure of the total amount of dust a filter is able to hold during a dust-loading test.
ASHRAE Standard 52.2-1999 measures particle size efficiency (PSE). This newer standard is a more descriptive test, which quantifies filtration efficiency in different particle size ranges for a clean and incrementally loaded filter to provide a composite efficiency value. It gives a better determination of a filter's effectiveness to capture solid particulate as opposed to liquid aerosols. The 1999 standard rates particle-size efficiency results as a MERV between 1 and 16. A higher MERV indicates a more efficient filter. In addition, Standard 52.2 provides a table (see Table 1) showing minimum PSE in three size ranges for each of the MERV numbers, 1 through 16.
Table 1 - Comparison of ASHRAE Standard 52.1 and 52.2
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ASHRAE 52.2 |
ASHRAE 52.1 |
Particle size |
Applications |
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Particle size range |
Test |
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MERV |
3 to 10 µm |
1 to 3 µm |
.3 to 1 µm |
Arrestance |
Dust spot |
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1 |
<20% |
- |
- |
<65% |
<20% |
>10 |
Residential - Larger than 10.0 microns. Light Pollen, Spanish moss, dust mites, sanding dust, paint spray, dust, textile fibers, carpet fibers |
|
2 |
<20% |
- |
- |
65-70% |
<20% |
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3 |
<20% |
- |
- |
70-75% |
<20% |
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4 |
<20% |
- |
- |
>75% |
<20% |
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5 |
20-35% |
- |
- |
80-85% |
<20% |
3.0-10 |
Commercial buildings, better residential, industrial workplace, paint booth inlets. 3.0 to 10 microns. Mold, spores, hair spray, cement dust, snuff, powdered milk |
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6 |
35-50% |
- |
- |
>90% |
<20% |
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7 |
50-70% |
- |
- |
>90% |
20-25% |
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8 |
>70% |
- |
- |
>95% |
25-30% |
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9 |
>85% |
<50% |
- |
>95% |
40-45% |
1.0-3.0 |
Superior residential, better commercial buildings, hospital laboratories. 1.0 to 3.0 microns. Legionella, lead dust, milled flour, coal dust, auto emissions, nebulizer drops, welding fumes |
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10 |
>85% |
50-65% |
- |
>95% |
50-55% |
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11 |
>85% |
65-80% |
- |
>98% |
60-65% |
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12 |
>90% |
>80% |
- |
>98% |
70-75% |
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13 |
>90% |
>90% |
<75% |
>98% |
80-90% |
0.3-1.0 |
Hospital inpatient care, general surgery, smoking lounges, superior commercial buildings. 0.30 to 1.0 micron. All bacteria, most tobacco smoke, droplet nuclei, cooking oil, copier toner, face powder, paint pigment |
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14 |
>90% |
>90% |
75-85% |
>98% |
90-95% |
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15 |
>90% |
>90% |
85-95% |
>98% |
~95% |
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16 |
>95% |
>95% |
>95% |
>98% |
>95% |
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