High-Efficiency Whole-House Air Filtration System

Systems that are placed in the central HVAC system and filter over 90% of allergens and other pollutants from the air.

The United States Environmental Protection Agency (EPA) estimates that indoor air pollution levels can be from two to five times higher than the outdoor air. Along with this, they estimate that some people spend up to 90% of their time indoors. Typically, particles 10 microns in size and larger get caught in the nose and throat, but are expelled by coughing and sneezing. However, many particles, including allergens,can be as small as 0.1 microns. These can become embedded in the lungs and have long lasting negative health effects.

There are many different types of air filters that can clean these smaller particles from the air, and they can be installed in your central forced air heating and cooling (HVAC) system to provide filtration for the entire house. High-efficiency air filters greatly reduce the number of airborne particles when compared to the standard 1-inch thick filter installed on most central HVAC systems. Some high-efficiency models can even filter out tobacco smoke, airborne bacteria and allergens to some extent. Whole house filters are usually placed in the return duct line adjacent to the air handler for easy installation and maintenance. The air handler pulls air through the return ducts, and consequently through the filter. The air-filtration method can vary, and sometimes different methods are combined into a hybrid system.

• Mechanical or surface media filtration is the method by which pleated air filters capture particles. Filtration occurs through a dense matted fiberglass media that captures airborne particles. The fiber material is pleated, allowing considerably more surface area. More surface area improves the filter’s efficiency and useful life. Typically, pleated filters are set in stages (more than one pleated surface) to provide more filtering material. HEPA filters are very efficient pleated versions. They are tested to ensure that they capture at least 99.97 percent of particles that are 0.3 microns in diameter. They are even more efficient at capturing larger particles. Some HEPA filters are combined with activated carbon filters to allow them to absorb pollutants such as cigarette smoke.
• Electronic air filtration makes use of electrostatic precipitation. Electrostatic precipitators charge particles and pull them out of the air stream. It can be a one- or two-stage system. In a one-stage system, a plate or other surface both charges and attracts the particles. In a two-stage system, the particles are charged in stage one as they flow past a set of charged wires or corona fields, and then attracted to an oppositely charged plate or grounded media filter as they flow through in stage two. Many electrostatic precipitators claim to have efficiencies of over 90 percent, with some as high as 98 percent for allergens like pollen.

Many filters combine mechanical and electronic filtration. The flow first passes through a pleated fiber pre-filter to remove some of the larger particles, then through an electronic precipitator, removing smaller particles.

Manufacturers claim varying rates of particle efficiencies for their systems. Particle efficiencies are made based upon ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) testing standards. Ratings are given either in a percentage or a MERV rating (Minimum Efficiency Reporting Value). Percentage ratings must be given for particle size ranges and MERV ratings go from 1 to 16, taking particle size ranges into account. MERV is an industry-standard rating, so it can be used to compare air filters made by different companies. Some manufacturers also have their own rating systems. The following table details ratings based on the ASHRAE standards for air filtration.

MERV Std 52.2	Average ASHRAE Dust Spot Efficiency Std 52.1	Average ASHRAE Arrestance Std 52.1	Particle Size Ranges	Typical Applications	Typical Filter Type
1-4	<20%	60 to 80%	> 10.0 µm	Residential Minimum- Light Commercial Minimum- Equipment Protection	Permanent / Self Charging (passive) Washable / Metal, Foam / Synthetics Disposable Panels Fiberglass / Synthetics
5-8	<20 to 35%	80 to 95%	3.0 – 10.0 µm	Industrial Workplaces Commercial Better- Residential  Paint Booth / Finishing	Pleated Filters/ Extended Surface Filters/ Media Panel Filters
9-12	40 to 75%	>95 to 98%	1.0 – 3.0 µm	Best- Residential Better- Industrial Workplaces Better- Commercial Buildings	Non-Supported / Bag Rigid Box Rigid Cell / Cartridge
13-16	80 to 95% +	>98 to 99%	0.30 – 1.0 µm	Smoke Removal General Surgery Hospitals & Health Care Best- Commercial Buildings	Rigid Cell / Cartridge Rigid Box Non-Supported / Bag
17-201	99.972 99.992 99.9992	N/A	≤ 0.30 µm	Clean Rooms High Risk Surgery Hazardous Materials	HEPA ULPA

Maintenance of these filters depends on filter type and particle load, but is typically less frequent than standard 1-inch forced air system filters, which must be changed up to several times a year. Media filters, depending on type, have to be either replaced or cleaned, from once to twice a year. Some HEPA filters require even less frequent replacement (sometimes once every two years). Electronic filters have to be cleaned or wiped down, and the frequency varies by product and manufacturer. One manufacturer recommends cleaning every three to nine months, depending on use. Pre-filters on these devices may have to be changed more frequently than the primary filter needs cleaning.

High-efficiency whole-house air filtration systems help improve indoor air quality. Poor indoor air quality can lead to negative health consequences.

Ease of Implementation

Whole house filtration systems can be installed during or after construction. The only requirement is that they be located in the return line between the air handler and split off (if it exists) in the return line. With media filters, it is important to realize that they create a pressure drop and consequently lower the airflow. This often requires a more powerful fan in the air handler to maintain a proper volume of airflow. In this sense, it is imperative that someone size the fan and filter to ensure a properly operating system. Typically, with all other things being equal, the thicker the pleat (e.g. 4” instead of 2”) the lower the pressure drop will be, and the higher the filter efficiency the higher the pressure drop will be.

Initial Cost

Initial system costs vary significantly between types. ESP filter units can range from $150-300; HEPA units can range from $500-900 depending on size; and electronic units can range from $350-1,500, depending on the design, components, and the number of stages.

Operational Cost

Operational costs include replacement filters and any power consumed by the electronic filters. Many typical 1-inch filters for furnaces cost between $3 to $15. Replacement ESP filters are typically around $25 to $30, and HEPA filters can run up to $150. Electronic systems usually consume less than 60 watts while being used, adding $10 to $50 per year to the homeowner’s electrical bill.

U.S.Code Acceptance

The IRC does not make any specific reference to air filtration in the central HVAC system. The American Society of Heating, Refrigeration and Air conditioning Engineers (ASHRAE) publishes standards to which these filters should be tested and implemented. Another rating organization is the Clean Air Delivery Rate established by the Association of Home Appliance Manufacturers. It takes into account the amount of clean air the system is able to provide. Also, be sure products are tested to ensure their safety through organizations such as Underwriter’s Laboratories.

Installation

Systems should be installed in an easily accessible place between the air handler and the return registers. For electronic filters, close proximity to a power source is recommended. Many installations occur immediately before the return line enters the air handler. Depending on duct cross-section geometry, a transition from the duct to the filter and back to the duct may be required in order to maximize the filtering and airflow.

Warranty

Limited warranties are generally from 2 to 5 years, depending on manufacturer and filter type.

Benefits/Costs

Due to the number of pollutants and potential allergens in indoor air, filtering the air from a central point can be very beneficial to occupant health. It eliminates the need for multiple portable filtration units throughout the house. Having a central electronic filter will also reduce the power consumed and noise produced from multiple room units. These filters also perform significantly better than typical 1-inch air handler filters and have fewer maintenance requirements. However, their cost is higher than typical filters and they filter air only when the air handler is on, so individual room filtration control is not possible. Electronic filters are known to create small amounts of ozone, though not in levels typically considered hazardous to human health.

Disclaimer: The information on the system, product, or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the U.S. Department of Housing and Urban Development (HUD/FHA), The Partnership for Advancing Technology in Housing (PATH), or any PATH-affiliated Federal agency or private company. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.