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Committees - Indoor Air

Clearing the Air - One Room at a Time

by Sarah Borwein, Jun 2000

When the air pollution levels soar in Hong Kong, do you hide inside with the aircon on high? Did you know that indoor air can be more seriously polluted than outdoor air, even in very dirty cities? In fact, the Environmental Protection Agency in the United States estimates that indoor air is two to five times as polluted as air on the other side of the window. What's more, we spend as much as 90% of our time indoors, so the risks to health may actually be greater from the pollution in our homes and offices than from the streets of Causeway Bay.

The causes of indoor air pollution are many. Not only does outdoor air find its way into our homes, and sometimes concentrate there, but we add to it with tobacco smoke, gas stoves (especially if they are unvented, as they often are in Hong Kong), pressed wood, dust mites and cockroach antigen, molds and mildew, animal dander and saliva, and fumes from carpet adhesives and upholstery. Inadequate ventilation worsens the problem, and high temperatures and humidity can increase concentrations.

So what can be done to improve the quality of the air we breathe inside? First, and most important, is source control. Maintain your gas stove properly, vent it to the outside and don't smoke. Next, make sure you have adequate ventilation. Closing all the doors and windows to keep out Hong Kong's dirty air does not help, and may make things worse. And as an adjunctive measure, air cleaners can offer significant relief from indoor air pollution.

What to consider when buying an air cleaner

The Technology

These days, three main types of technology predominate: mechanical filters, electronic precipitators, and ionizers. In the former, a filter, which may be flat or pleated, mechanically strains air of fine particles. High-efficiency particle (HEPA) filters can remove all particles down to 0.3 microns, while ultra-low penetration (ULPA) filters can remove even smaller particles. Precipitators work by passing the air through an electrical field where particles take on a charge and are then trapped on oppositely charged collector plates within the machine. Ion generators charge the particles in a room and then attract them to a charged collector plate. Ionizers do work, but can sometimes result in dirty walls, ceilings and furniture, as the charged particles adhere to these surfaces.

Many models these days are hybrids, involving two or more of the above technologies. In general pleated filter models (HEPA or UPLA filters) are the most effective at removing particles; however the top rated model tested by Consumers Reports used an electronic precipitator.

The CADR

The measure of success of an air cleaner is its Clean Air Delivery Rate (CADR), which depends on how well it traps particles, and how much air it moves. The Association of Home Appliance Manufacturers (AHAM) rates participating models according to their CADR, via its CADR program.

AHAM-certified air cleaners are given CADR-ratings for three separate pollutants: pollens, smoke, and dust. In this way, consumers can choose an air cleaner that is best at removing the pollutant they are most concerned about (in practice, the three figures are usually close). It is important to choose an air cleaner with a high enough CADR for the room requiring cleaning - size matters. The following chart gives some guidelines:

Room Size (in feet)

CADR for tobacco smoke

8 x 10 or less - 50
10 x 12 - 80
12 x 12 - 100
12 x 16 - 120
14 x 16 - 145
16 x 20 - 200
18 x 20 - 230
20 x 20 - 250
20 x 24 - 300
24 x 26 - 400

The manufacturers participating in the CADR program are:

Amway Corporation
Bemis Manufacturing Company
Blueair, Inc.
Carrier Corporation
DeLonghi America Inc.
Friedrich Air Conditioning Company
Honeywell Consumer Products
Hunter Fan Company
Hung Hsing Electric Company
Kaz, Inc.
Panasonic Consumer Electronics
Sunbeam Corporation
Trion, Inc.
The Holmes Group
Vornado Air Circulation System
Whirlpool Corporation
White-Rogers, Division of Emerson Electric Co.
Windmere Coporation

Appliances made by these companies should have a CADR rating which you can use to decide if it is an appropriate model for you.

Care and Upkeep

Like any appliance, air cleaners require upkeep to maintain optimal performance. HEPA and ULPA filters must be replaced about once per year, and are quite costly. Electronic precipitator models are cheaper to run because they don't require these filters; however their collection-plate assembly and prefilter must be removed from the machine and washed every month.

Convenience and Noise

Some models are very heavy, so if you will want to move it from room to room, wheels and handles can be very welcome. Noise can also be an issue. Some models are very noisy, and this can be extremely annoying. The CADR figure on the model assumes you will run it at high speed at all times, however you may well wish to run it a medium or low to reduce noise. In this case, you should buy a model with a higher CADR to allow for this.

Cost

Consider not only the price of the unit, but the energy costs of running it, and the upkeep costs for replacing filters. The top-rated model rated by Consumers Reports is the Friedrich C-90A, which is quite expensive to buy, but also energy efficient and inexpensive to maintain.

What's available in Hong Kong

I checked out Fortress, Wing-On Department Store, Sincere Department Store, and CRC Department Store and found the best selection of air cleaners at the lowest prices to be at Fortress. They carry Philips, Bionaire, Rowenta and Amcor and the occasional Honeywell. Only Philips and Honeywell carry a CADR rating. Unfortunately they do not carry any of the models rated highly by Consumers Reports and only Honeywell participates in the AHAM rating scheme.

The Philips models may be the best bet in Hong Kong. Be sure to pre-measure the room you are buying it for, and buy the model with the appropriate CADR rating (using the chart above).

Watch for Hype

Given the level of concern about air pollution in Hong Kong, it is not surprising that many manufacturers attempt to exploit fear and hype. One particular kind of air cleaner that is NOT recommended is the ozone generator, which is currently being flogged by several companies in Hong Kong. The United States Environmental Protection Agency has actually issued a position paper warning against these units. Ozone is good in the stratosphere, where is protects us from ultraviolet radiation, but is harmful in the atmosphere. Breathing it in can damage the lungs. Companies that sell ozone generators often call ozone "energized oxygen" or "pure air", which is misleading. Furthermore, if used at concentrations that do not exceed public health standards, ozone does not remove particles from the air, nor is it effective in removing carbon monoxide, formaldehyde, viruses, bacteria, mold or other biological pollutants. And even when used as directed, many models raise ozone levels in the room to levels that can be harmful to health. Ozone is a pollutant, not an air cleaner.

The Down & Dirty on Cleaning Indoor Air - What You Can Do

Install exhaust fans vented to the outdoors in kitchens and bathrooms
Vent clothes dryers to the outdoors
Make sure your gas stove is vented to the outside
Ventilate attics and crawl spaces
Regularly clean the evaporation trays and filters in dehumidifiers, air conditioners, and refrigerators
Clean and dry (or remove) water-damaged carpets and building materials
Keep your house clean and free of dust. (if you suffer from allergies, a HEPA filter air cleaner can be helpful)
Be careful to adequately ventilate rooms with gas space heaters
Consider room air cleaners, especially for bedrooms