A major advantage of forced air systems is the ability to filter air in addition to heating or cooling it. A number of filtration options exist. We will gladly review the options with you to choose the system that best meets your needs of efficiency, cost, and convenience.
The typical washable or throwaway type filter that comes with the furnace is usually satisfactory for larger lint particles and animal hair, but does little for pollen, animal dander, dust mite residue, mold spores, and other fine household dust. Many of these fine particulates stay airborne until they stick to the walls, furniture, or draperies, or until they are breathed in by the building’s occupants.
The simplest way to modestly improve indoor air quality is to replace the standard washable or throwaway media filter with a pleated filter. These will catch most of the visible dust and are several times more efficient than the standard filter. Our service department uses these pleated filters to replace existing standard throwaway filters when performing equipment maintenance.
Extended pleated media filters, such as the Lennox PMAC or Aprilaire 2410 provide even greater efficiency at a modest additional cost. These are very effective against pollens and dust particles 3 microns are larger. The media only needs replacement once a year, and the initial installation cost is low when replacing heating and air conditioning equipment.
Electronic air cleaners are even more efficient than the typical extended media filter. There are no consumables, but the cells should be washed every few months to maximize effectiveness. These operate by ionizing particulates while they flow through the system. A series of collector plates with several thousand volts of static charge then precipitate the ionized particulates, leaving very clean air returning to the living space of the home.
The Aprilaire 5000 electronic air cleaner is a hybrid between the traditional electronic air cleaner and the convenient extended media air cleaner. A charging grid ionizes particles that are drawn very efficiently to a grounded media. These boast some of the highest efficiencies in the industry.
HEPA filters are sometimes requested for non “clean room” applications such as residences. Although these have an extremely high efficiency rating (99.97%), they contribute too much resistance to air flow to be attached directly in the air stream of a typical ducted system. The HEPA systems use separate filter/blower cabinets that bypass about 50% of the airflow to be cleaned and returned to the air stream.
Not all air contaminants are in particulate form. Odors and chemicals such as pet odors, cooking smells, perfumes, tobacco smoke, chlorine, cleaning supplies, paints, and solvents cannot be removed by particulate filters. Bioaerosols such as bacteria, viruses, molds, spores, and fungi are not necessarily removed by these filters either. The Lennox PureAir(TM) air purification system combines a MERV 16 pleated media filter, UVA lights, and a catalyst to remove the widest spectrum of airborne contaminants available in a residential system
All of the systems we have described here mount on the return side of any forced air heating and/or cooling system. For maximum effectiveness, the fan must be running all of the time. Modern thermostats feature a fan switch for continuous air operation. Some models allow you to program continuous fan operation during specified periods. Variable speed blower motors provide the quietest, most efficient air circulation for air cleaning.