Offering an Efficient Filter for Improved Indoor Air Quality
July 9, 2007
Indoor air quality is an important issue for most homeowners today. Homeowners expect the air filter to protect the HVAC equipment as well as provide a clean, nearly dust-free environment. With this expectation comes a challenge: How to offer an efficient filter without having resistance so high that it causes problems with the homeowner’s heating and air conditioning system. Today’s contractor has a vast array of products to offer to the homeowner compared to just a few years ago.
The 1-inch pleated panel filter would be the most practical and inexpensive filter choice for most homeowners. These typically have a MERV value range of six to 11. In most cases, there is no upgrade of equipment required although some homeowners do need to be aware of the higher resistance to airflow so they can check and replace the filter more often. Contrary to most beliefs, 1-inch pleated filters in the home do not last longer than non-pleated filters. Pleats are more efficient; therefore, they arrest more particles than non-pleated filters and since these filters generally start with a higher resistance to airflow, the homeowner should change them before they start to cause problems like a frozen coil. Higher resistance will also lead to higher energy consumption and more wear and tear on the entire HVAC system. It is obvious with the growth in pleated filter sales in the U.S. that the consumer is aware of the air-quality benefits of a pleated filter but they may not be as aware of the potential resistance problem.
Another practical option for the homeowner is the high-performance return grille filter. These pleated filters are typically between 4 or 5 inches thick and are made in such a manner that they will fit into a standard 1-inch return grille without any modification or retrofitting as long as there is room for the back side of the filter (typically 4 to 5 inches). It has a 1-inch thick header and the thicker portion of the filter is recessed into the return duct or plenum. Most return grille filters have a MERV value range of eight to 11. The real beauty of this type of filter is its low resistance to airflow. It achieves this low resistance by having as much as five times more media (surface area) than the 1-inch thick pleated filter. The additional media also extends the life of the filter. It can last considerably longer than a 1-inch pleat.
Many homeowners are opting for the in-line whole-house media air cleaners. Typically, these units have a cabinet installed on the return side of the air handler and a 3- to 5-inch pleated filter fits inside this cabinet. To change the filter, the homeowner simply opens the cabinet, pulls the old filter out, installs the new filter inside the cabinet, and then slides the cabinet back into place. Whole-house media air cleaners tend to be very efficient with MERV values between eight and 11. Even with the high efficiencies, the resistance is relatively low. Moreover, like the return grille filter, the additional media (surface area) also extends the life span of the filter. Some newer models of the whole-house media air cleaner have provisions for a pre-filter, most commonly a carbon-type filter. The carbon adsorbs many odor-causing gases in the home.
In addition to the above-mentioned filtration methods for the home, there is another option. The “bypass HEPA” system is usually added downstream from the coil. It pulls a small percentage of conditioned air using its own fan from the trunk, pushes the air through a HEPA filter, and then reintroduces the cleaned air back into the main system. This system only filters less than 30 percent of the air that the air handler moves for one primary reason; residential systems cannot handle the resistance that a HEPA presents. HEPA filters generally have seven to eight times more initial static pressure than a 1-inch pleat. These systems are typically used in situations where a person in the home has respiratory problems.
The indoor air of modern homes can be much more polluted than the outside air but thanks to many of the air filters and filtration devices available today, our homes are cleaner, healthier, and more energy efficient than ever. Luckily, homeowners are actively seeking these products and contractors to install them.