I'd have to disagree with all of your statements. Not only are they derived from no experience in the field, you are missing keys facts. Ducts even if air tight will get dirty. If they are not getting dirty, it means they are not working. Your returns side of the duct work is always under negative pressure when the system is operational.Therefore it is always drawing air in. Seeing how dust is made up mostly from dead skin humans shed daily. Around 1.6 Pounds of skin a year per human. Living in your home anything that is air born will be drawn back towards the cold air returns. That is what they are designed for, to draw stale air back to the system to be filtered and sent back through the house.Homes with carpet will actually have cleaner duct work than home with all tile or hardwood. This is because carpets hold onto dust particles and you vacuum them up. Whereas on hardwood or tile, dust can run freely back to the returns. Even if a duct system was sealed 100%, which is next to impossible to achieve 100% would still need to be cleaned. The cleaning may only have to be every 7-10 years for example. Most homes require every 5-7 years. And that's if it was done properly the first time. If you constantly hire people that have no or minimal knowledge of duct cleaning, You home would require cleaning more often. Every 2 years. That's a trade secret, The longer they recommend before the next cleaning, the odds are they did it right. That's not to say there aren't people that lie, because there are. Just have your duct cleaner take pictures before and after cleaning. Not just an outside view. Get in there, picture entire joist liners, Whole main runs and even long round pipes. Also it helps to have a company that guarantees their work. If it's not done right, they will come back and do it until it is. Most companies that do this make sure it is right the first time. Your not getting paid to do the job twice.
Sounds like your first hvac company was ripping you off. Ask your new company to go to your coil and see if there is a leak. If there isn't the last company was just lining their pockets. If you have had ducts unhooked for a long time I would recommend duct cleaning, trust me I'm not a fan of duct cleaning myself. I have done hvac for 20 yrs. in GA. When I just bought a home built in 1996, we had all the ducts replaced immediately.
Since most states and municipalities don’t license air duct cleaners, you need to check their professional credentials instead, such as NADCA membership. EPA recommends all duct cleaners follow NADCA standards. Member companies must keep at least one technician on staff who has passed a NADCA test. “They have to pass rigorous testing to earn the certificate, and our code of ethics is very important,” Vinick says.
I can’t believe I got ripped off by this Air Duct Cleaners. I called them for this $63 coupon per furnace unlimited vents then when they came after he checked it all I hear is I have molds and leak all is worth $499, $799, $899 per furnace but I told him to just clean the duct and patch the single leak per furnace worth $38 each. Still eanding $899 total. All the work he done is in less than an hour he didnt even go to each vent to clean it. All he did is to path the air leak on that entry pipe to the furnace and open the main venting system, vacuum it, and wash the floor of the vent with a solution. Overall time is about 20 mins talking with me discussing all the option which thinking they made me think I don’t really have an option and 40 mins wash and vacuum he took pictures of before and after of only one furnace. He gave me a receipt without the details on what he has done in the house just the name and price. I think we may need a strict law to punish and control all this companies who do this so other company who do good will despise them.
Some research suggests that cleaning heating and cooling system components (e.g., cooling coils, fans and heat exchangers) may improve the efficiency of your system, resulting in a longer operating life, as well as some energy and maintenance cost savings. However, little evidence exists that cleaning only the ducts will improve the efficiency of the system.