As a qualified duct cleaning contractor I have discovered that most homeowners feel that they are very uninformed when it come to the principals and practices of proper air duct cleaning hygiene.
Let me begin by saying that the EPA as well as the National air duct cleaners association have stated that residential duct cleaning should take no less than between 4 and 8 hours to complete, anything short of that and you are probably not getting a thorough job.
Consumers are cautioned against duct cleaning companies that claim to be able to clean your entire air duct system in a very short period of time and for an unrealistic low price, in this industry that kind of service is completely unacceptable and is known as the blo-n-go style of duct cleaning.
Remember...anything short of between 4 and 8 hours and you are probably not getting what you're paying for.
Many homeowners are also under the impression that the main ducts and primary vents are the only components that require cleaning, However this is not the case, a thorough duct cleaning must include any internal surface in which the air moves across, this not only includes the main ducts and vents but must also include the conveyance compartment of the furnace/AC, heat exchanger, AC coils, drain pan, blower, filter housing and any air cleaning equipment that might be installed.
The only acceptable method of proper air duct cleaning is to put the entire system under negative air (vacuum) by means of a powerful vacuum system that produces no less than 2000 cubic feet per minute of air flow (cfm), each individual vent shaft should be cleaned using a combination of high pressure air snakes, rotating brushes and whips which must be driven by a compressor that will deliver no less than 175 psi @ 12-16 cfm.
In conclusion, when choosing a qualified air duct cleaning company be sure to ask if they their technicians and equipment meet the above criteria and always get a few references, it is also recommended that you contact your local better business bureau or chamber of commerce.
Duct Cleaning Could be the Healthiest Home Improvement You Will Ever Make!
Pat Johnson - President of Enviro-Pure Air Care Duct Cleaning, located in Ottawa, Ontario, Canada