Why do you think you air ducts need to be cleaned? In most cases it is not necessary. Many air duct cleaning services offer services for low prices and do very little in actually cleaning.

Cleaning ducts or anything for that matter with mold on it is not fixing anything. The mold will come back within a few months in most cases. In order to fix the problem, you must find the cure.

The cure is often more expensive than merely cleaning.

The duct cleaning company mentioned on this page is AFAIK, not licensed to work on or repair HVAC systems. Legally as long as all they do is duct cleaning and follow the Texas requirements listed at the bottom of this page -- this is perfectly fine. BUT, you must ask yourself... do you really want an unlicensed company working on the most expensive system in your home?

Most of the dust and dirt that gets into your HVAC system is very fine dust with very small particle buildup over years of use. The dirty pictures they show is most often the air return that is often unfiltered up to the furnace in which the furnace typically has a large media filter installed.

Usually the low price is geared to get their foot in the door and then upsell you things like insulation, radiant barrier, UV lights and so on. While some of these may benefit you to some degree you must still fall back to the line in which I say 'the company is not licensed'... because if what they do is not performed properly there is little benefit.

If the duct(s) got dirty once and all you do is clean them, they will get dirty again. The best approach is to hire a licensed HVAC contractor and look for solutions that actually fix the problem.

Texas licensing requirements:

(c) Duct cleaning. (1) Duct cleaning and air quality testing, including biomedical testing, may be performed by a person or entity that does not hold a contractor license under Texas Occupations Code Chapter 1302 if: (A) the task is limited to the air distribution system, from the supply plenum to the supply grilles of the unit and from the return air grill to the air handler intake of the unit; (B) no cuts are made to ducts or plenums; (C) no changes are made to electrical connections; and (D) the only disassembly of any part of the system is opening or removal of return and supply air grilles, or registers that are removable without cutting or removing any other part of the system. (2) Biomedical testing may be performed by a person or entity that does not hold a contractor license under Texas Occupations Code, Chapter 1302. (3) Biomedical remediation requires a contractor license under Texas Occupations Code, Chapter 1302.