Whole House Purifiers vs. Portable
The perfect theme song for the whole house air purifier controversy is Tobacco Road, written by John Dee Loudermilk in 1960, and covered by numerous artists:
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A central "whole house" air purifying system, added to existing heating, ventilation, and air conditioning (HVAC) equipment, is NOT the cost effective solution for household air quality.
Unless you are wealthy and/or building a new, carefully custom designed home, this cash is best spent on other aspects of the indoor air situation.
I do not claim a whole home air filtration system, beyond a simple furnace filter upgrade, is not a good idea for those with extra cash.
Note that everyone, including apartment dwellers, should install a furnace filter upgrade.
A MERV-7 filter or better is highly recommended. Ordinary fiberglass furnace filters cost just $.75, and upgrades are $5-20.
I'm pretty sure anyone reading this thinks their health is worth more than the cost of a furnace filter upgrade.
But no wholehouse HVAC system is a substitute for properly selected room air purifiers placed close to our breathing zone.
This article will focus on the shortcomings and cost effectiveness of air purifiers for an entire home that add on to existing HVAC systems.
Notice that air duct ultraviolet light systems, for defense against microorganisms, are considered separately.
Consumer Reports, in a 1992 issue, said portable air cleaners are more effective than a central whole house system.
Here is one of the few topics where I agree with CR's air cleaner reviews.
Since such a filtration system shares the central system's blower and duct work, the first concern must be the wholesomeness of the HVAC (Heating, Ventilating, Air Conditioning) internals.
In my opinion, dirty HVAC systems and duct work are second only to wet, moldy basements, in the “Nightmare on Elm Street” awards.
HVAC Duct Inspection:
How many of us ever remove our home's vent louvers and inspect our ductwork, raise your hands.
That's not very many.
So how many want to do it today?
Oh, that's better.
Who wants to go first?
Nobody?
OK, I'll do it myself.
In the photograph, taken in my old Houston apartment, the red arrows point
to accumulated fine dust which has come through the fiberglass air filter over the years.
The blue arrow indicates a new section of duct wall which has less dust.
Because this dust has been screened by a coarse air filter, whitening of the duct wall is the more dangerous fine particles!
The lower red arrow points to dust I piled up with my finger.
Yuck! Are we done yet?
Fiberglass HVAC air filters are placed upstream of motors and fans to protect them from sandpaper-grit sized particles and lint, not as air purifiers.
No expensive upstream filter or partial bypass whole house air cleaner can do anything about this accumulated mess!
HVAC Blowers
HVAC blower systems, while they may seem powerful, with maybe 1000 cubic foot per minute (cfm) airflow, do not set up a strong enough air current in most areas of the household to be meaningful air purifiers.
Stand near the airflow from an AC duct, you won't get blown away.
The airflow right at the duct is about as strong as a small table fan.
A quality portable air purifier creates strong internal pressures. Air-Purifier-Power is focused on how this pressure is handled in air purifiers of varying quality, and how many builders solve the problem by allowing bypassing.
Air from central system registers does not flow evenly through the cross section of the home, it seeks the path of least resistance.
Cooled air makes a beeline straight to the bottom, without visiting the out of the way 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 larger particles fall out.
While the house as a whole may receive several air changes per hour, the net result in the lower flow areas is not strong enough.
Imagine a meandering stream, with surging bank cuts and rapids, followed by lazy drifts over sandbars; the speed is not uniform across the whole stream.
Varying sizes of particles, from silt to gravel, are deposited where water slows accordingly.
In a house, dust bunnies collect in corners where air slows.
This is not an effective model for air purifiers.
With a central purification system, the blower must run all the time.
Residential HVAC blowers are not powerful enough to draw air through a big, tightly sealed, whole house HEPA air filter.
In fact they must be protected from overloading which could occur with an ordinary dirty furnace filter.
Real HEPA filters create serious static pressure, so they cannot be installed inline with the standard residential system.
Vendors have incorporated costly bypassing vent circuits and more powerful secondary filter blower mechanisms to get around this.
This is nothing but a high dollar version of the bypassing I cry about every day in cheap, loosely built department store air purifiers!
Who'd pay to replace what ain't broke?
This has created a marketing opportunity for add-in ionizers, ultraviolet sanitizers, and electrostatic precipitators, which are less restrictive.
Some of these create ozone.
Duct Cleaning:
Cleaning your whole air conditioning air handler system and duct work could be the best single indoor air quality improvement money can buy.
It depends on how old the system is, how much moisture is present (mold loves to hide on AC condensers and in drip pans), and when (if) it has been cleaned before.
Don't assume a brand new home has clean duct work.
Air ducts will collect dust during construction.
Site cleanup is a hidden cost on every job, and with subcontracted crews coming and going, you never know what might be in hidden areas of a new house.
You can hire a professional duct cleaning service to vacuum and clean the air vents and ducts.
It isn't cheap and must be done carefully without toxic chemicals.
Add Room Air Purifiers when Clean
Once the system is clean, install an upgraded quality air filter in the HVAC main air return or air handler.
I line the edges with polyurethane foam to limit bypassing.
Regular maintenance is required to keep the whole house system clean in the future.
Cost Effective?
"I'll get some money, be rich I know, and bring it back to Tobacco Road"
Wholehouse air purification runs from just expensive to shoulda-got-the-Mercedes-instead expensive, requires installation by a contractor, and uses significant electricity to run both blowers continuously.
Replacement costs of pre-filters and filters will match or exceed room purifiers.
Many buyers are disappointed with their central household air filtration installation, only to find that the vendor and contractor each blame the other for the problem.
We take our central air conditioning systems for granted, out of sight and mind. Adding purification could change that.
When a portable air purifier fails, we ship it back without interruption of heating or cooling.
You cannot return unsatisfactory home modifications to a vendor.
To get the best indoor air quality, I would;
remove all toxic sources,
ventilate often,
completely clean HVAC system including duct cleaning,
install upgraded furnace filter,
use premium VOC capable room air purifiers in bedrooms,
put less expensive HEPA filters elsewhere.
With any funds left over from the alternatives listed above, I suggest installing a central vacuum system for the entire house, which exhausts 100% of all dirty air outside.
Or chose a quality sealed HEPA filter vacuum cleaner.
For new construction, I'd skip the carpet, get hardwood and tile floors and powerful central vac.
In the downtown apartment, I have installed urea foam prefilter material (cheap at Wal-Mart) in my air vent louvers. I believe this has reduced larger particles in the outflow air.
I use several portable air purifiers as a system, and run the A/C on hot days only.
Air Purifiers at Amazon.com.
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