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The HEPACART Blog

Why the MERV Rating on Your Negative Air Machine Matters

A negative air machine is an integral part of any complete dust containment strategy, whether used separately or in conjunction with a portable dust containment cart. But how do you know if the one you choose is working as effectively as possible? One way is by considering its MERV, or Minimum Efficiency Reporting Value. This value tells you how effective the  machine is at removing certain particles from the air.

How MERV Ratings Apply to Negative Air Machines

Negative air machines work by creating negative air pressure in order to force potentially contaminated air through its filtration in order to removed the offending particles. So what is a MERV rating, anyway? MERV is a tested value, established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), that indicates how effective a filter is. The MERV rating on a negative air machine, therefore, will refer to the MERV rating on that machine's filter.
 

What Should Your MERV Be?

When using negative air  in a high-risk construction environment, it should be equipped with a HEPA or ULPA filter. These filters will have a MERV of greater than 16. However, it should be noted that some negative air machines have a design that allows for multiple filters. A pre-filter may have a lower MERV. By utilizing a machine with this type of construction, you may be able to extend the life of the HEPA filter in the machine. 

Generally speaking, a HEPA filter is more costly than a less efficient filter, largely due to the cost of HEPA filter testing. Because a pre-filter with a lower MERV will be able to remove many of the particles in the air before the HEPA filter is engaged, the HEPA filter will last longer with greater efficacy. Of course, be sure to follow all containment guidelines when it comes to the filtration you use.
 

Choosing the Right Negative Air Machine

The right machine should be one that is compatible with your dust containment needs as well as any dust containment carts, ceiling access carts, or anterooms that are in use. When using a HEPA filter, the precise MERV is usually not taken into consideration as long as the filter is certified.

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