Featured in the IASBO Update October 2000

The cost of Indoor air quality has been a hard thing to define. Everybody wants it but nobody can put a finger on exactly how much it costs and what you get for the investments you make to keep your schools a ”healthy” place in which to learn and grow. There is a new breed of filter that takes a positive step toward improving IAQ. In doing so, these filters address many building operating and maintenance issues. The following identifies specific costs of air filtration, defines terminology used to compare filter effectiveness, the characteristics that make these new filters out perform all other filters in its class, and the financial benefits of using this new breed of multi-layered filter.

First Cost

The first question asked is, How much does the filter cost? If the proposed filter costs five cents more than what is being used today, the incentive to buy it falls right into the wastebasket. Filter costs are complicated by the numerous types of filters on the market. For a 500,000 square foot school, the annual costs for filter media can run into the thousands of dollars.

First Cost Also Includes Labor

First cost also includes the cost of labor to install the filter. All filters are not equal. If you have rigid cardboard-framed filters, they may not be easy to get in….or out. If you buy filters by the roll and cut filters to size there is considerable labor associated with pulling the metal support cartridge (not to mention the cartridge cost), cutting and installing the media in the cartridge, and putting the cartridge back into place. If you apply a spray anti-microbial to the media to kill mold and bacteria imbedded in the filter, there are additional labor and material costs.

If you use your maintenance staff to pull cartridges, cut and replace media, apply the anti-microbial, and reinstall the filters, your annual costs can run $6,000.00 for labor alone. (@ $25,000/year plus 40% for benefits =$35,000. 3 weeks/ change X 3 changes = $6,000.)

Additional Costs - Heating and Cooling Loss, Cleaning, and State Aid

First costs of materials plus the labor associated with filter change outs are not the only costs associated with filter selection. The cost of dust, mold & bacteria build up on coils, ducts & rooms are additional real costs. The performance of the filter media has a great impact on exactly how much we pay. Poor filtration deteriorates heating and cooling capacity. Taken to the extreme, dirt, mold, and bacteria build up form a “cake” on the coils that block off airflow into classrooms. (This opens a whole new set of problems with fresh air intake, O2 and CO2 levels that are topics outside the scope of this article.) Coils and ducts cost thousands of dollars to clean. The amount of State Aid a School District gets is a function of student attendance. Absenteeism is very expensive.

Filter Performance - the One-Two Punch

Filter performance and construction have a great deal to do with the cost of operating and maintaining facilities. The one-two punch is to trap and then to destroy trapped microorganisms. To compare filters, let us look at the terminology that is used to describe filters.

Capture Dust, Mold, Bacteria, and Mildew

Destroy Trapped Microorganisms

Without a proper anti-microbial agent, filters become breeding grounds for trapped mold, bacteria, and mildew, which occur in the 1.0 to 10.0 micron size range. These microorganisms when airborne can spread infectious illnesses.

Physical Characteristics of the New Multi-layered Filters that make them the Filter of Choice!

Comparison of Filter Performance Tests

(run by an independent lab - ETL)

Fiberglass Throw Away Filters

Pleated Filter W/ Microbial Multi-Layered Filter
Have no ETL Rating Arrestance 91.3% Arrestance
90.6% Have no ability to capture particles below 10 microns until the filter Loads PSE - 81% of 3 micron PSE
79% of 3 micron No Rating below 10 micron DHC
183 Grams@ 1.0
WG final DHC
154 Grams@ 1.0
WG final

The multi-layered filter performance is comparable to a pleated filter. Fiberglass filters are ineffective in capturing particles below 10 microns and consequently, provide a limited ability to stop the spread of infectious illnesses.

New breed of Multi-layered Filter - Physical Characteristics

Compared to Pads and Frames

Internal wire support frame prevents sagging, even under the worst humid and moist conditions. No gaps between filter segments means no bypass. No spacer blocks are needed either to fill a row..

Compared to Pleats

Financial Benefits of using Multi-layered Filters

The financial example given below is for a 500,000 square foot school.

Figure 1 lists comparative prices for three types of filters with the lowest cost being fiberglass throwaway filters. Pleated filters cost three times as much. The new breed of multi-layered filters cost twice as much. Figure 2 shows an annual budget projection for three change outs per year. .

Figure 1 - The Filter Figure 2 - Annual Filter Budget
Fiberglass throw away			$1.75*
Pleated w/ microbial			$5.25*
Multi-layered w/ microbial		$3.80
*Based on a 24” x 24” x 2”
Fiberglass throw away			$4,500*
Pleated w/ Microbial			$13,500*
Multi-layered w/ microbial		$9,750*
*Cost of three change out

Real Costs after the Filters are installed

After filters are installed, performance of the filter in terms of its ability to trap and destroy microorganisms has a significant impact on how a building operates and the cost to maintain building comfort and health. Additional costs include; Loss of Building Performance, Increased Coil, Duct, and Room cleaning, and reduced State Aid.

Building Performance

In Figure 3 below, loss of building performance caused by as little as 0.006” of dirt( approximately the thickness of 3 pieces of paper) can reduce heat transfer by as much as 16%.

Figure 3 - Excessive Gas & Electric Bills – 500,000’2  School
Thickness of scale (inches)	.000	.006	.012
% Loss of heat transfer		0	16%	20%
Boiler NG cost 			*	0	$8,600	$10,800
Chiller Electric cost	*	0	$19,200	$24,000
Total  Utility Cost			0	$27,800	$34,800
Total gas cost is $60,000 per year.  90% of this total consumption is
for heating the boilers   which heat the school = $54,000.
*Total electrical usage is $400,000 per year.  30% of this total
consumption is for running the chillers.


Coil and duct cleaning, dusting of computer labs and equipment, and reduced financial aid from the State caused by absenteeism are also real costs affected by filter selection. Continuing with our example of a 500,000’2 school:

Coil Cleaning @ $60,000. Done Every 5 years = $12,000/year average.

Increasing the interval between cleaning cycles by 50% to 7.5 years, reduces annual amortized costs by $4,000.00 Duct Cleaning @ $100,000. Done Every 10 years= $10,000/year average. Increasing the interval between cleaning cycles by 50% to 15 years, reduces annual amortized costs by $3,000.00


Each student gets~$4,600. Absenteeism caused by air born illnesses of 3% in a school of 2000 reduced to 2.5% can increase state funding by an estimated $46,000.00. Dusting computer equipment and labs is a real expense. The size of this cost is very school dependent. TBD


A new breed of filter technology is available that outshines fiberglass filters and performs like a pleated filter in independent lab tests but at 2/3s the price. The gasketing features and linked panels made these multi-layered polyester filters superior performers. The real cost of indoor air quality includes more than the initial investment in filter media. Labor to change-out filters, excess energy use caused by clogged coils, the cost for frequent coil and duct cleaning, and the impact airborne illnesses have on absenteeism are also real costs associated with filtration. The impact this new breed of filtration can have on a 500,000 square foot school is listed below.

Summary of Incremental Costs

By upgrading filters to the new breed of multi-layered polyester filters, the increase in filter cost of $5,250 over fiberglass throw-away filters produces a net savings of $78,000.

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