Yes, ducts can look terribly dusty. However, that dust will not become aerosolized during the normal operation of your furnace. There is an easy way to test this. Rent a particle counter and test the air flowing out of your registers before and after cleaning. You will not see any improvement in the air quality or any reduction in the airborne dust level. Think of it this way. Duct cleaning companies tell you that you need to clean your ducts when you can see a layer of dust in your ducts. Yet that very layer of dust is proof that duct cleaning is unnecessary, because that dust proves that the air movement in your furnace is not fast enough to re-aerosolize the dust.
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.
I live in a 1950's ranch house in the South. The prior owners were smokers. Based on recommendations from one of the local conservation organizations, I decided to have a home energy audit done. As part of their findings, they recommended additional insulation in the attic and duct cleaning and sealing. This turned out to be a very problematic process. In terms of the ducts, it was necessary to remove the metal grates. However, these grates had been painted over many times and shoe molding covered the bottom of the grates. The vendor was not able to remove the grates without damaging them in the process. Because these grates dated back to the 1950's, it was difficult to find appropriate replacements. The ones I finally discovered were correct except they were 1/4" wider. This meant that the shoe molding had to be carved out. The duct cleaner could not provide any assistance with this problem. It took me a month of long evenings replacing the vent covers myself, carefully chiseling out the shoe molding and repainting. In terms of the extra installation in the attic, the same vendor used blow in insulation. Unfortunately, they did not recognize that the 13 floodlights whose mounting extended into the attic were not designed to be buried under insulation. The problem manifested itself in terms of expensive flood light bulbs failing continually. So, I had to have all of the light housings replaced. Yet another unexpected expense. Despite the expense, pain and suffering, I cannot report any improvement in my heating costs or the "quality" of the air. To be fair, I do not have any allergies and did not undertake this for air quality improvements but rather heating efficiency improvements.
Although i love to burn candles, depending on the type your asking for problems big ones! At work one day i had been talking with co workers about these black shadows that were appearing on my ceilings and higher wall areas. They seemed to in the corners and along the stud supports , i could even see what i thought to be where all had been nailed. There would be dark shadows perfectly straight across my ceiling and then real dark circels every few inches within the lines. I thought it was the propane heat but learned quickly that oil heat will do that but not normally propane. A co worker brought me a magazine with a huge article about candles and what actually burns off them when lit, an ashy soot that is attracted to the areas on walls and ceilings that omit the most heat or warmth, of course where the drywall and studs meet and corners of the room. Its been about 8 years since i painted the entire house. I started bending to my love for candles again in the last 3 years, surprise i will be spending part of my summer re painting again!! No more candles ,well maybe at the holidays LOL
A thorough visual inspection is the best way to verify the cleanliness of your heating and cooling system. Some service providers use remote photography to document conditions inside ducts. All portions of the system should be visibly clean; you should not be able to detect any debris with the naked eye. Show the Post-Cleaning Consumer Checklist to the service provider before the work begins. After completing the job, ask the service provider to show you each component of your system to verify that the job was performed satisfactorily.
I hired duct cleaning company out of "Service Magic" website. I did not realize the name of his company was Duck cleaning of Central Florida...that should have given me a hint.. The guy did a very poor, incomplete job, and ruined a closet full of clothes when he sprayed up to clean a vent instead of taking it down and cleaning it outside. He left me with more than 1/2 dirty vents and ducts, did not do the air handler in the garage and failed to fog the system. He spent 6 useless hours at my residence and now his insurance is denying coverage..very disappointed in Service Magic....
Just had my air ducts cleaned. They used a high pressure air hose in all the heat ducts and cold air returns. He showed me the stuff that came out, the reason for the duct cleaning was the fact that I had a problem. With rodents. There was quite a few mummified rats and mice, and he said I wouldn’t have to have them done again unless I incur another problem or have renovations done. Cost me 345.00 for a 2 storey large old home. Not a bad price as I had them done when I moved in 28 years ago and it cost me 500.00. Lots of dog hair, toys, balls and assorted goodies came out as well. Took them 2 hours. I did have sanitizer put in the ducts because of the dead rodents.
If the one noticeable spot is where the wall [or ceiling or floor] is white.......first.....take a pair of needle nose pliers and bend each louver of the register to a straight outward position [as they all come brand new with a slant to each side]....so the register is shooting all supply air straight outward. If its a round register [in ceiling].....no help there. You also should always burn soy or beeswax candles.
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.