MERV 11 Air Filter – The Compromise Efficiency

MERV 11 Air Filter – The Compromise Efficiency

It could be that because we’re in the Midwest and it’s part of our culture more than other places, but we are always seeking a compromise between High-Quality and Price.  Never thinking we deserve the “best” and compromising with “good enough” has lead to high demand of MERV-11 air filters.  But is MERV-11 really Good Enough?  Is MERV-13 really the Best?  We’ll atempt to answer these questions

When it comes to air filters the number one conern should be – What does it remove from the air, and how does that align with my IAQ goals?  To answer that we can quickly remove many air filter effieicncies/MERV from consideration – and the MERV 11 air filter should be one of those removed.  Here’s why:

Whether your goal is equipment protection or occupant health it fails.

This graph shows the distribution of particles that are in the air – to no real surprise the smaller particles are the ones that stay suspended, or “floating” in the air while larger particles settle.  99% of all particles found in the air are smaller than 1 micron.  At that particle size a MERV 11 air filter only removes 20% which isn’t enough to really offer health benefits to building occupants.  For protection of HVAC coils ASHRAE has long put forward that anything MERV-7 or higher is adequate as the “average” HVAC system without filters will accomplish MERV-6 with its coil.

So if you want to provide better Indoor Air Quality MERV 11 air filters fall short and you should really consider a minimum of MERV-13 which takes out over half of all sub-micron particles and possibly incorperating a carbon filter to remove Ozone, Nitrogen Oxides, and other common molecular pollutants.

If equipment protection is your primary goal, than it is overkill to use a MERV 11 air filter as it takes out more than needed to keep your HVAC equipment adequately clean – which is why specifying/design engineers still write a lot of equipment specifications to have only MERV-6 or MERV-8 filters.

Have Your HVAC Filters Audited

But The Removal Efficiency Chart Makes MERV 11 Look Like a Good Middle Ground

YES!  The MERV table makes filters look far better than what they are because it is an arbitrary scale with arbitrary ratings that have changes 4 times in the past decade.  A MERV-8 is in the exact middle of MERV, yet removes less than 5% of airborne particles.  Between how the current 52.2/MERV system misleads air filter buyers and the global Air Quality Community using Particulate Matter (PM) measurements to determine air quality have prompted forward thinking air filter companies to develop and adopt ISO 16890 which has been approved in every country outside the US and Canada – and if it gains approval here will replace the very misleading 52.2/MERV system.

Even after all of this – there is a place for filters that achieve MERV 11.  In spaces that have a source generation of particles, like manufacturing facilities, it is possible that this would be the appropriate filter to use.  It’s just that the real world applications where it fits is small and it should not be used for general HVAC purposes. 

In reality MERV 13 is the compromise filter for IAQ.  This is because it removes a minimal amount of particles to have a positive impact on air quality, but does not offer any filtraiton of molecular pollutants that have far more damaging long-term health effects.  Particles by themselves don’t tell the whole story in IAQ – something that has been either ignored or forgotten by most air filter sales people.

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