Hi Dave, thanks for the great question about filter requirements at VAV boxes for LEED certification.

LEED for Air Filters: MERV Requirements

The credit that applies to the MERV requirement for air filters is Indoor Environmental Quality (IEQ) Credit 5: Indoor Chemical and Pollutant Source Control.

This credit requires that “each ventilation system that supplies outdoor air” be equipped with a filtration device rated a minimum efficiency reporting value (MERV) of 13 or higher.

When VAV boxes (a.k.a. “terminal units”) are part of your HVAC system, this requirement can be, understandably, a little fuzzy.

Variable Air Volume: Types of VAV Boxes

First, we have to determine what kind of VAV boxes your facility has. If they are simple “damper-only” VAV boxes, then the answer is simple. Since these units get all of their air from the air handling unit (AHU), the filter on the AHU will suffice, as long as it meets the requirement of IEQ Credit 5.

This would also apply to VAV boxes with reheat coils, provided the VAV boxes do not bring in air from other non-filtered sources.

Fan-powered VAV boxes are a different story. These boxes usually pull in and re-circulate air from the space around the VAV box, which is often “return air” from the plenum (space above the ceiling) destined to be recirculated in the AHU. Because this air has picked up pollutants from the interior space, the LEED review team will insist that these boxes are equipped with filters with a MERV 13 or higher rating.

Air Filters and Energy Efficiency: Law of Diminishing Returns

Unfortunately, these highly effective filters make fans work harder to push the air through, thereby consuming more fan energy, or requiring a larger horsepower fan. The law of diminishing returns will govern at some point, and the points you are looking to achieve in Energy and Atmosphere Credit 1: Optimize Energy Performance may suffer because of the level of filtration required by IEQ Credit 5.

To summarize: if you have “damper-only” VAV boxes, they won’t need filters, and you’ll likely be able to achieve IEQ Credit 5 with a MERV 13 filter on the AHU. If you have fan-powered boxes, the additional filtration that would be required at each terminal unit might not be worth the trouble it takes to earn the credit.

I hope this helps!

Related Advice:

• LEED EQ Credit 5: Are MERV 13 Filters Always Required?



• Water Filtration: Does MERV Apply to Water Filters?



• What is a Variable Air Volume (VAV) Box?