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  • Writer's pictureConnexFM

Filtering the Facts

ConnexFM releases a new white paper focused on HVAC filtration.

Although air quality has been recognized as a vital issue since the 1970s, the pandemic has only further highlighted its importance. This is evidenced in the number of building operators across the country expressing an interest in upgrading their air filter efficiency.

The reasons for upgrading air filtration are many, from new code requirements and government recommendations to providing proof of clean air to occupants to avoid future liability concerns. But, with existing equipment, there are many considerations to keep in mind before making the switch to a higher-efficiency filter. To help FMs understand the topic, Ron Prager, Executive Vice President at Brinco Mechanical Management Services, wrote a white paper about HVAC filtration, with its most important points summarized below.

A MERV Rating Refresher

HVAC systems with packaged equipment are all equipped with some type of filtration and are typically fitted with U channels that can accommodate 2-inch-thick air filters. The efficiency of these filters is measured and given a minimum efficiency reporting value (MERV) rating corresponding to how effectively the filter stops particles, like dust or allergens, from going through the filter and into the air. The higher the MERV rating, the more effectively the filter can trap small particles. Ratings run from 1 to 20. To standardize, most manufacturers rate their equipment with MERV 4 filters. A common high-efficiency choice is MERV 13.

The size of the pores in the filter media and the layering of the media determine air filter efficiency. As the pores decrease in size, the efficiency increases, as does the resistance to airflow created by the filter. The HVAC industry measures this resistance in pressure units defined as inches of water column (WC).

Increasing air filter efficiency increases the pressure drop across the air filter substantially, increasing the static pressure the blower must overcome and making the blower work harder. Because of this, some systems that were rated with a MERV 4 filter will not be able to accommodate one rated MERV 13. For those that are capable, this upgrade will likely require adjustment to the blower sheave or replacement of the sheave and/or blower motor to operate with higher-efficiency air filters.

What to Expect

For operators looking to upgrade, they need to understand why it is more complex than simply swapping in a new filter and what those potentially adverse effects on unit operation could be. If equipment is compatible with more-efficient filters, there are many considerations operators need to keep in mind:

· High-efficiency filters are significantly more costly than MERV 4 filters (see Figure 1).

· Regardless of the efficiency rating, some air will bypass the filters.

· The use of higher-efficiency air filters may increase energy usage and demand.

· Availability of MERV 11 and 13 filters can be an issue due to high demand.

· Unless a test-and-balance report for the existing equipment is available, the external static pressure the equipment is currently operating at is unknown, so it is extremely difficult to determine in advance what adjustments must be made or what components must be replaced prior to installing high-efficiency filters. Hire a certified test-and-balance contractor to adjust the system to accommodate the increased pressure drop caused by the new filters, and determine if sheave replacement is required.

· More-efficient filters will load more quickly than MERV 4 filters and may require replacement frequently. Because of a variety of factors, it is difficult to predict how often higher-efficiency filters will require replacement.

Prepping for Install

Once building operators have determined they will upgrade the filters, indoor coils and blower wheels should be cleaned prior to upgrading to minimize resistance to air flow through the unit. To easily monitor the new filters, try the filter upgrades in a small number of sites in different geographic locations. Inspect the new filters at 30-day intervals to determine how fast they are loading and how frequently they will need to be replaced. If a building is equipped with an energy management or building automation system, the operator should monitor the discharge air temperature on equipment where filter efficiency was upgraded to determine the effect of the new filters and how quickly they are loading. These recommendations should ensure the upgrades run as smoothly as possible and achieve the desired indoor air quality.

Read the White Paper

Access the full HVAC Filtration white paper at


The Unfiltered Truth: HVAC Air Filtration Series

The COVID-19 pandemic has resulted in a surge of questions, recommendations and code-required changes with respect to indoor air quality. Increased ventilation, higher-efficiency air filters, bi-polar ionization and ultraviolet germicidal irradiation are now being considered (and implemented in some cases) by building operators. Watch this three-part series, where HVAC experts share the indoor air quality knowledge you need to help make the right decisions for your facilities.

Visit to watch the series today!

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