A whole house air purifier system, added to existing central HVAC equipment, is not a cost effective solution for home air quality.
With the exception of those who can afford both types, our money is best spent on other aspects of the indoor air quality situation.
Since such a filtration system shares the central system's blower and ductwork, the first concern must be the condition of the HVAC (Heating, Ventilating, Air Conditioning) internals and ducts.
Dirty HVAC systems and ductwork will spew fine particles. Adding an expensive upstream filter system will not change this.
Standard fiberglass HVAC air filters are installed ahead of motors and fans to protect them from sandpaper-grit sized particles, not as air purifiers.
Central HVAC blower systems, which may seem powerful, with up to 1000 cubic foot per minute (cfm) airflow, do not set up a strong enough air current in most areas of the house to be good air purifiers. The air flow at the duct is about as strong as a small fan.
Air from whole house registers does not flow evenly through the cross section of the home, it seeks the path of least resistance. Cooled air cuts a path straight to the bottom, without sweeping the upper nooks and crannies.
Warmed air fans out along the ceiling until it finds a cool surface to start a downdraft. Where corners, steps or obstacles are encountered, eddies form and particles accumulate. While the house as a whole may receive many air changes per hour, the net result in the lower flow areas is impure air.
Picture a meandering stream, with surging bank cuts and rapids, followed by lazy flats with sandbars; the velocity is not uniform across the whole stream. This is not an efficient model for air purifiers.
With a whole house purification system, the HVAC blower must run all the time. Home HVAC blowers are not powerful enough to draw air through a large, tightly sealed, whole house HEPA air filter. They must be protected from overheating which might occur with an ordinary dirty fiberglass furnace filter.
HEPA filters create serious static backpressure, so they cannot be installed directly into the standard residential system. Vendors have incorporated costly bypassing vent circuits and more powerful secondary filter blower mechanisms to get around this. Partial bypass systems are grossly inefficient, allowing dirty air to bypass through the main duct.
Air duct cleaning, an expensive job for fully qualified professionals, should be considered before a whole house air purifier installation is purchased. Many consumers are unhappy with their central air filtration installation, only to discover the vendor and contractor passing the buck to the other.
We take our central air conditioning systems for granted, out of sight and mind. Adding a whole house air cleaner could change our perception. When a portable air purifier fails, we return it without interruption of heating or cooling. You won't be returning unsatisfactory home modifications to a vendor.
Old folk wisdom applies here: "If it ain't broke, don't try to fix it."
For best indoor air quality; remove all toxic sources, ventilate often, clean HVAC system including coils, pans and ducts, upgrade present furnace filter, use premium chemical-capable portable room air purifiers in bedrooms, put less expensive HEPA air purifiers elsewhere.
With additional money where available, consider installing a central vacuum system for the whole house, which exhausts 100% of all dirty air outside. Or choose a quality sealed HEPA filter vacuum cleaner.
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The Author, Ed Sherbenou, is an experienced air purifier user, with 40 years of direct experience due to chemical sensitivity and severe allergies. He writes indoor air quality articles, posts blogs, and maintains a leading air purification website:
http://www.air-purifier-power.com