First of all, let me point out that IAQ complaints and illnesses, most of which are real, don't always come from the same sources. Many people are allergic to dust mites and roach droppings, others are sensitive to chemicals, another group is affected by mold and some are allergic to everything. So promoting a single idea as a cure-all for IAQ problems is pretty silly. And that's where the scam comes in.

A very popular product that gets contractors into the air quality business is the duct-cleaning machine. And that's a good start, because air-conditioning equipment and ductwork are important sources of IAQ problems. However, if the company only cleans the ducts, they may do no good at all or make the problem worse. You see, all duct-cleaning machines do is remove dust, mold and bacterial buildups from the ductwork. And in the process, they may loosen fiberglass liners, creating an airborne fiber problem. Also, few contractors go to the lengths needed to completely clean every square inch of ductwork, which is required, and if they don't do anything to clean the interior of the cooling equipment or sanitize and seal the cleaned ducts, the treatment does no lasting good.

My recommendation on duct cleaning is to purchase small, portable units with HEPA exhaust filters, since they can also be used to pressurize areas where sensitive IAQ mitigation is being done. After cleaning and sanitizing the entire ductwork system and air handler, everything must be sealed using an anti-microbial paint.

Air filters do a lot of good when it comes to improving most types of air-quality problems, but which do the most good? Of course, since I don't operate a testing lab, all I can give you is an opinion. The throw-away filters most people use are mainly there to protect the evaporator coil from large pieces of dust. And while using filter sprays does cause them to pick up more dust, this usually results in the chemical being added to indoor air, which may do more harm than good. However, filters designed to pick up dust mites or roach feces, mold spores, fine particulates, etc., are a good idea.

For years a battle has been raging among companies that manufacture media, electrostatic and electronic filters. In my opinion, if someone is replacing a 1-in.-thick throw-away filter with something you can't see through, the replacement creates too much static loss to be a viable idea, even when there is some pleat to the filter. Media filters with a pleated surface and which are more than 4 in. deep may be the best choice to improve air quality, if they are changed often enough.

Electrostatic filters, which are said to create an attracting static charge from the air passing through it, don't seem to be a good idea to me. I have found that most have too much static-pressure drop and the principle doesn't appear right, at least during the cooling season. I know that many contractors -- and customers -- love them. However, at the 50% relative humidity that you'll find in most air-conditioned rooms, I doubt there is much of a static charge in the air.

I've heard many negative comments about electronic air filters, but in my experience they work well. I've cleaned units in the homes of people who smoke. And believe me, if you ever had to do that, you'd never smoke. There is no question that these filters remove huge quantities of air-quality pollutants.

When it comes to removing odors and chemicals, however, nothing beats activated charcoal filters. They have to be sized and installed properly to ensure minimal pressure drops. They also have to be reactivated regularly by baking. However, I doubt that those filters that have a few bits of charcoal glued to their surface really do much good.

What about chemicals you spray on evaporator coils and in the ductwork to kill mold and bacteria? They have some value for localized use, but nothing you spray in ducts will work permanently without creating chemical IAQ problems. This is also my concern when it comes to ozone generators.

Ozone will clean up the insides of air conditioners and ductwork because it's a bleaching agent. That feature also makes it harmful to breathe. However, this treatment method may have merit if it's designed and applied right.

Another product for ductwork is ultraviolet lamps. I'm sure this is a good idea, particularly when the lamps are mounted in the upstream side of the air handler, shining on the coil. UV light definitely kills mold and bacteria, and eliminating problems at the evaporator and drain pan are good ideas. I've seen devices that create both UV light as well as ozone for the downstream ducts, and that sounds like a winner to me.

Of course, air conditioners can be the source of IAQ problems as well as solving them. The fact is that if you can keep the indoor air below 50% relative humidity, dust mites become less of a problem. Therefore, systems that are designed with deeper evaporator coils for more latent cooling are very helpful in improving air quality. However, they are often the source of mold spores when they aren't kept clean or when water blows off the coils into the ductwork.

Another product that I saw about two years ago is a coil that mounts in the ductwork downstream from the evaporator. You hook the refrigerant liquid line between this device and the evaporator. The warmer coil after the evaporator raises the discharge air's leaving humidity, which tends to keep the ducts dry and free from mold or bacterial growth. In turn, the cooler liquid line to the evaporator causes the coil to run cooler. So, while there is little difference in the actual system capacity, more moisture is removed and the ducts are dry.

This method, along with good filtration, a UV light source and regular system cleaning, looks like the best total IAQ package.