What is a HEPA filter?

My Opinion and the Dirty little truths.

Unfortunately, the word “HEPA” has become a bit of a common word and used by many companies as a buzz word. Technically speaking it stands for “High Efficiency Particulate Air” and according to the “Institute of Environmental Technology” (IEST) they define the filter as being made into a rigid frame and having a minimum efficiency of 99.97% on particles of 0.3 micron in size. While the USA standard has been based on the IEST standards the rest of the world tends to lean towards the European standard EN1822. ISO standard 29463 is based on European standard EN 1822 and will probably replace this standard in the future. Both standards are based on the latest particle counting methods but there are light differences between them.

With out putting everyone to sleep I will move on to the bigger issues. So everyone that makes an air cleaner or a vacuum cleaner these days wants to say they have a HEPA filter. I have seen some filters that would barely meet a MERV13 that were stated as a HEPA filter and I have seen one U-Tube video with a guy in a lab coat pretending to be a doctor and he places a 1” thick filter over a $25.00 box fan and says it’s a HEPA.

I fear that the misunderstanding will eventually get some one into trouble or endanger lives. There are additional criteria besides the fact that every HEPA filter (each individual one) should be tested before it leaves the factory. The next step is that once the filter has been transported and mishandled, it is imperative that the filter be placed into a proper housing that will provide even compression against the filter to get a good seal on the gasket. Some HEPA filters utilize a fluid seal (of course good and bad points) that is point of discussion by itself. So when you see a filter in a paper frame and it has no gasket. It will not give you HEPA quality. You must be able to get a good seal with even compression on the gasket. So even though most large companies test the filters and say they are made in accordance with the IEST standard for HEPA’s they have all pushed the envelope. The last time I read the standard it called for the filter to be made in a 16 gauge frame or a 3/4” particle board or plywood frame. Most of that reason was so that you could place enough pressure on the filter to get that positive seal on the gasket. So most factories slowly moved to an 18 gauge frame to save on metal cost and the weight of the filter. Now many of the factories all offer HEPA filters made in a 24 gauge metal frame that I can bend with my fingers. So be careful to ask about the frame or to specify that the frame is 18 gauge minimum. Many new HEPA’s are now made in a plastic frame. Not all plastics are created equal but most of these are made heavy duty enough that they will allow for proper compression when force has been applied without any loss of integrity to the filter.

Finally if you really needed a HEPA, in real life after the filters are installed a separate person arrives after the filters are installed and test the filters in place to make sure that the filter is sealed in place and there are no leaks. So if you are being told you are buying a HEPA filter for your house or for a small piece of equipment beware if it is in a paper frame or the gasket is an open cell material that will allow air to come through it. It will not test as a true HEPA.

If you are purchasing your HEPA’s under the EN1822 standard make sure you ask for a minimum of H13 efficiency. That means each filter had to be individually tested to meet the H13 rating.

Clean Liquid Systems LLC
Don Palermo CAFS

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