I own a small mechanical company. My main work is service and system replacements. I have never been a believer in duct cleaning. The company I worked for before had our duct man come out and do my house. I saw no difference. Preventive maintance is what I recomend. Remove fan and clean, seal fan compartment to prevent dust from being pulled in, filters I install media filters, they are 5″ thick and pleated. I have tested them to make sure static presure was not a issue. Heat exchangers and AC coils need to be cleaned. I will tell you this to do a good cleaning I usually spent 1-2 hrs, When I’m finished I would not have a problem eating my diner on the system. Good filters, clean system and properly tuned up are my recomdation to anyone. I’ve included my email feel free to contact me with any questions. winkcfd@yahoo.com
Their crew arrived promptly at 7:00 am. Carlos explained what each crew member would be doing. They increased the insulation in my attic. They also discovered that the ducts had been attached to the vents with plain duct tape. The duct tape had become gooey due to heat and had slipped off the vents in many places. This allowed out side air and dust to enter, spreading dust out of the vents. It also allowed cooled air to escape into the attic. The corrected all of the duct work connections. Jeff came to check the work upon completion. He ran tests to verify that the work had been done correctly, and he replaced all of the "regular" light bulbs with cal bulbs. All of the work was done quickly and neatly.
Duct cleaning generally refers to the cleaning of various heating and cooling system components of forced air systems, including the supply and return air ducts and registers, grilles and diffusers, heat exchangers heating and cooling coils, condensate drain pans (drip pans), fan motor and fan housing, and the air handling unit housing (See diagram).

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Pay particular attention to cooling coils, which are designed to remove water from the air and can be a major source of moisture contamination of the system that can lead to mold growth. Make sure the condensate pan drains properly. The presence of substantial standing water and/or debris indicates a problem requiring immediate attention. Check any insulation near cooling coils for wet spots.
Demonstrate visible evidence of microbial growth in your duct work. Some service providers may attempt to convince you that your air ducts are contaminated by demonstrating that the microorganisms found in your home grow on a settling plate (i.e., petri dish). This is inappropriate. Some microorganisms are always present in the air, and some growth on a settling plate is normal. As noted earlier, only an expert can positively identify a substance as biological growth and lab analysis may be required for final confirmation. Other testing methods are not reliable.
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I guess I should present my credentials first, I am a 30 year veteran of the heating and cooling industry. I started at the bottom and have participated in every area of the trade. Installer, service, maint. Ownership, rep, territory manager and so on. A forced air duct system is a large vacume. Like your vacume it has an air intake (return air) and an exhaust (supply registers). A filter just like a vacume (located next to furnace or air handler). Now I want you to visualize something. Put your head inside your vacume cleaner and breath. Get the picture? This is what your duct work looks like. Do you clean your vacume when it’s dirty? If it’s full and the filter is dirty you lose performance and it starts poluting the air you breathe. It’s common sense. I recommend hiring a duct cleaning outfit that you have researched to be honest, background checked, drug tested, insured, and highly recommended by your piers in the area. The service is a necessity, but like everything, it should be done by a qualified company.
Washington Consumers’ Checkbook magazine and Checkbook.org is a nonprofit organization with a mission to help consumers get the best service and lowest prices. We are supported by consumers and take no money from the service providers we evaluate. You can access Checkbook’s ratings of local HVAC companies free of charge until Feb. 28 at Checkbook.org/washingtonpost/ducts.
15 vents and ducts cleaned for the firest time since house built in 1968. Charles and his wife came at 8:00 am as scheduled, with their enormous vacuum, conneded it to our system, removed all the vents, plugged them with sponge material and vacuumed the entire system while they scoured out all of the aire conditioneing ducts from end to end with a rotating brush with flexible bristles like a string trimmer that reached all of the crevices in the ducts. While Charles cleaned the ducts, his wife cleanted all of the vents. they sanitized and deodorized the entire system. They finished everything and cleaned up and left just before noon. I examined the ducts after they left and they gleamed like new. $304 well spent and excellent service. I'd recommend them to anyone.
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.