EPA 402/B-20/006
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Indoor airPLUS Technical Bulletin
Fi tration
High efficiency filters help remove small particles from the air that can cause adverse health effects, so upgrading HVAC
filtration has the potential to make important improvements in indoor air quality for homeowners. What this means is that
your homeowners can breathe better every day knowing their home is equipped to help manage a critical respiratory
contaminant — airborne particles.
Selecting the Right Filter
The home's heating, ventilation, and air-conditioning (HVAC) system regularly recirculates indoor air, distributing and
redistributing dust, pollen, mold spores, pet dander and other indoor air contaminants. Air filters should be installed not
only to help protect the HVAC system components, but also to remove particulates and improve the overall air quality
indoors. Filters should also be installed in fresh air intakes to clean outside air that is brought into the home.
Air filter efficiency is graded using the MERV rating, a scale based on test methods established in ASHRAE Standard
52.2, although some filters may be graded by their manufacturers on alternative proprietary scales. MERV stands for
"Minimum Efficiency Reporting Value." A typical 1-inch-thick spun fiberglass furnace filter has a rating of 1 to 4 on the
MERV scale and can trap particles like sawdust, carpet fibers, dust mites, and pollen.
Indoor airPLUS currently requires filters to be at least MERV 8. These
filters can generally clean the air of contaminants such as cement dust,
mold spores, animal dander, hair spray, and most of the larger particles
that are 3-10 microns in size. However, filters with higher MERV levels are
available and recommended by EPA to more effectively remove smaller
particles (PM2.5), which are of greatest health concern.
Filters with a MERV of 11 remove roughly 20% of the particles between .3 and 1 micron, and a MERV 13 filter typically
demonstrates at least 50% removal efficiency for the smallest particles tested. High Efficiency Particulate Air (HEPA)
filters with MERV ratings from 17 to 20 are more effective at filtering out smaller particles, including viruses. However,
higher MERV filters do tend to restrict airflow. So builders and HVAC contractors wishing to install them must carefully
size the ducts and filter box to allow for thicker or wider filters, which generally create less static pressure and help
improve air flow.
As we continue to learn more about the benefits of particulate reduction indoors, and as improved filters are becoming
more accessible in the market, EPA plans to increase the filtration requirements in future versions of the Indoor airPLUS
Construction Specifications.
How to Design Systems with High MERV Filters
•	Design (or require the HVAC contractor to design) the HVAC duct system using ACCA Manual D to determine the
maximum static pressure that the filter can have and select a MERV 8 or higher filter within that limit.
•	Use the highest rated filter that your system fan and filter slot can accommodate. Consider adjusting the duct size,
duct length, and/or filter width to ensure that the total pressure drop across the system does not exceed the
blower fan motor's limit, given the size of the unit.
•	Design the filter slot on the return side of the HVAC air handler with an appropriate seal to ensure that there is no
path for airflow around the filter.
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EPA 402/B-20/006
Proper Installation of Furnace and Air-Handler Filters
Filters with higher MERV ratings can trap pollutants like pollen, dust
mites, and mold spores. However, a dirty, clogged filter can dramatically
reduce airflow, increasing furnace run time, wear on the motor, and
energy consumption. For optimum operation of both the filter and the
HVAC equipment, the filters should be replaced or cleaned frequently.
How to Design the HVAC System with Filter Replacement in Mind
•	Locate the filter where it can be easily accessed by the
homeowner for replacement or cleaning, without obstruction by
other appliances, fixtures, or mechanical components.
•	If the filter is installed in a filter media box attached to the air
handler, the access panel for the filter should be fitted with a
flexible, air-tight gasket to prevent air leakage.
For more details and best practices related to filtration, download EPA's guidance on air cleaners and air filters or visit the
Indoor airPLUS technical guidance on the Department of Energy's Building America Solution Center for more information.
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