In some older homes, there was a grey Mylar flexible duct. After years of use, it started to decompose. A duct cleaning company can come out and find why your air is so dirty and why your building doesn’t heat or cool like it used to. This is a savings on your part. You could also be sucking in Hot, dirty attic air. However, sometimes when a duct cleaning company comes out to clean it, the old duct can be destroyed and have to be replaced. Someone with little experience can replace this ductwork but if it isn’t done right it can ruin a lot of things and cost a lot in repairs.

This article was very good. It should be noted that the EPA building in Washington, DC, was cited years ago as one of the worst "sick building syndrome" buildings. Wish you had mentioned about having people's dryer vents cleaned since they can cause so many fires in homes. Most homeowners forget to check the air flow on the dryer vent. Our company, which cleans by NADCA standards, does both air ducts and dryer vents. Thanks again for keeping the public informed, especially regarding the cost of air duct get what you pay for...don't be fooled by the lowest cost out there. Frequently these are bait and switch companies or will keep adding on features they say a customer needs until the price is so high it's ridiculous.

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.
In addition, the service provider may propose applying chemical biocides, designed to kill microbiological contaminants, to the inside of the duct work and to other system components. Some service providers may also suggest applying chemical treatments (sealants or other encapsulants) to encapsulate or cover the inside surfaces of the air ducts and equipment housings because they believe it will control mold growth or prevent the release of dirt particles or fibers from ducts. These practices have yet to be fully researched and you should be fully informed before deciding to permit the use of biocides or chemical treatments in your air ducts. They should only be applied, if at all, after the system has been properly cleaned of all visible dust or debris.
You've probably noticed many appliances boasting an Energy Star Certification. What this means is that manufacturer voluntarily built the product to help reduce greenhouse gases and meet non-regulatory guidelines offered by the Environmental Protection Agency. To earn an Energy Star rating, a product or system must be tested by a third party that has been recognized by the EPA for meeting their testing qualifications.
I recently replaced my 44 year old furnace. Over the years we have had several construction projects inside the home. For many years breathing the heated air from the duct work caused excessive sneezing, sinus issues, and lung irritation. . The heat smelled like dust. To maximize air quality I added a humidifier, MERV-11 filter, and UV light onto the new furnace. To further improve air quality, I had the ducts cleaned and sanitized. I took before and after pictures of the inside of each return and output duct. They were filthy before, and sparkling clean and fresh after the procedure. Now when running the system, clean sanitized air flows through my whole house. A huge difference. It will make sleeping and being indoors during the winter months far more tolerable. I use window air conditioners, and run the system in the summer to keep the house air clean and fresh on hot summer days too. It works! Great decision!
2. If air quality is so important and duct cleaniliness is so uncertain, why not adopt doubling filtering; that is, in addition to the existing main furnace filter, add a filter at each air outlet. I understand replacing so many filters would be a burden, but air outlets can be designed for easy filter replacement. The builders and home design engineers should bear responsibility to provide good and low maintenance homes, rather than prioritizing on fancy or costly featuers for homes.
I am in need of HVAC ADVICE!! I need a new furnace badly, mine is cracked. I have bought both a 95 % AFUE furnace and a 5 Ton evap coil, I figured it should all be replaced at once for both cost and efficency. My question is with all the negaitive things I have heard about companies ripping you off, what type of price should I pay someone for putting in those two items and bringing everything in my attic up to code? I have been quoted $550 - $ 3300. Wide margin here!! Then of course comes the licencing part!! I know in my heart that I should use a licenced contractor but I have had such bad luck and prices from them that honestly one that was licened in Ga. and just not here in TN and is a tech. which charges 1100 - 2200 less sounds good as so long as I pay some type of Profenial HVAC person say $100 to inspect the work after its done and before I pay them.
If you’re purchasing from a big-box store, you can expect to pay approximately $120-$1,000 for a window unit. Window units are appealing for their quick setup and relatively low cost, but they can use more energy over time than central air and only cool the room in which they’re installed. The price will vary depending on the type of air conditioner you buy and its cooling capacity. Window units, which require minimal installation, are one of the most affordable options on the market. Portable air conditioners don’t have the cooling power of a window unit, but they do have the perk of being transportable from room to room. Expect to pay between $225 and $800 for a portable air conditioner, on average. The cost of an air conditioning system with coils, condenser and line (not including installation or ductwork) can range from approximately $2,000 to $4,000 or more. If you don’t have (and don’t want to put in) ducts, a ductless mini-split air conditioner is a good option, although pricey up front. Pricing can range from $650 to $4,250 per unit on average; you’ll need one unit for each room in which you want temperature control.
SEER is useful for comparing one model to another much in the same way that a car's calculate MPG is useful. It's not an accurate prediction of exactly how efficient the system is, but it can tell you which one is more efficient. Also, since SEER is based on a "cooling season", what region you live in will determine how long or short your cooling season is.
I call to follow up at the end of the next day and she said that she has not been able to get in touch with the owner.  By this time, I am starting to get frustrated because I am starting to get the run around.  I question her if I am even on the schedule or if they attempted to schedule a crane.  She says they are extremely busy and that she does not know.  So I say, basically I have waited over 2 weeks and you have not put me on the schedule and I am at the end of the install line.  No answer.  I tell her to talk to her boss and find out what is happening, and I will think about what direction I want to move in at this point.  

Duct cleaning has never been shown to actually prevent health problems. Neither do studies conclusively demonstrate that particle (e.g., dust) levels in homes increase because of dirty air ducts. This is because much of the dirt in air ducts adheres to duct surfaces and does not necessarily enter the living space. It is important to keep in mind that dirty air ducts are only one of many possible sources of particles that are present in homes. Pollutants that enter the home both from outdoors and indoor activities such as cooking, cleaning, smoking, or just moving around can cause greater exposure to contaminants than dirty air ducts. Moreover, there is no evidence that a light amount of household dust or other particulate matter in air ducts poses any risk to your health.