I am a service technician [since '92].....and as to double filtering.....I have never recommended it. Granted.....it would be noticeably helpful if the fiberglass filters are the main ones used [which I also never recommend.....as long as system can deliver appropriate air flow with a pleated cotton filter...and any decent service tech can check the air flow for proper cfm]. Any particles small enough to pass through a pleated cotton filter are going to pass through a second filter as well....unless the second filters are so tight that the system is starving for air flow. Has anybody ever accidentally put two filters in their automatic drip coffee maker? What if cars used two fuel filters or air filters? I have told some homeowners to try using second filters at each register [the black thin filter material cut-to-fit....same type used in many window air conditioners].....but I only suggest this when I know they will still get at least 400 cfm per ton of air flow [350 absolute minimum]......as some homeowners know others who say it has helped and it gives them a peace of mind knowing they are doing something to help contribute to a solution, so it HAS to help [even though I think it falls in the "one-born-every-minute" category.....similar to duct cleaning].

Did not realize cost had gone up so much for this service. Two years ago I had furnace and ducts cleaned at my old house and it was under $400. Now the cost is $700 for this house. I will keep looking for someone to offer a lower price, check them out, and have it done. Or will find the paperwork to see who did it before. I liked this article and did learn some things. Thanks.
PickHVAC Tips: Oil burns dirty, so it is important to have your plenum and ducts checked to see if they should be cleaned when replacing an oil furnace. If you don’t clean the plenum and ducts when replacing the furnace, the new furnace might not run as efficiently and comfortably as possible due to restricted airflow. This can also reduce the oily smell sometimes associated with oil furnaces.
I’m really not convinced that duct cleaning is of any value. My roommate wanted the ducts cleaned so he called some company. My scam senses is already tingling. They came in with a big negative pressure fan. Did some blowing and sucking in different vents. Then they tried to upsell a full system cleaning. They wanted to pull the blower and clean the heat transfer box at $700 per heater unit. I have a big house so we have two units. They also tried to sell us some “custom” $250.00 Air Lifetime air filters. At that point I pulled the BS get the hell out bell. After paying $520.00 for just the cleaning, I paid the bill and sent them on their way. I replaced the existing filter with the good old and cheap paper filters at $10.00 each. Duct cleaning… I’m not Impressed.

The HVAC industry is a worldwide enterprise, with roles including operation and maintenance, system design and construction, equipment manufacturing and sales, and in education and research. The HVAC industry was historically regulated by the manufacturers of HVAC equipment, but regulating and standards organizations such as HARDI, ASHRAE, SMACNA, ACCA, Uniform Mechanical Code, International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement.
These factors are included in a "Manual J" calculation. Contractors who make these calculations before recommending a size can take a couple of hours collecting the information and making the calculation. If your contractor doesn't do it, there are services that will do it for around $99. If you're feeling particularly on the ball, there are also free online calculators.

To qualify for a tax credit from the federal government, you must save the manufacturer's certificate from your system. The IRS won't require the certificate at the time you file your federal tax forms, but they recommend keeping it with your records in case of an audit. It proves that you purchased a qualifying product. The government offers tax credits for:
The short answer is yes, duct cleaning, done right by a reputable company will help with the smell. It is likely though the smell is coming from another source, ie the crawl space. It could also be that another rodent is dead in the duct work. A visual inspection would be in order to check for any breach in the duct system. A duct pressure test would be able to tell you how much air is leaking from the system over all. A hole large enough for an animal to enter would loses a great deal of air, over 300 CFM. It would be worth looking into having this test done and it should cost around $200. Cleaning the air handler and evaporator coil will greatly improve the performance of the air conditioner. Dirt and dust on the evaporator acts as insulation and reduces the amount of cooling done be the coil. Any quality duct cleaning should include cleaning the air handler and coil, and the tech should allow you to watch him perform the work as it is done.
The short answer is yes, duct cleaning, done right by a reputable company will help with the smell. It is likely though the smell is coming from another source, ie the crawl space. It could also be that another rodent is dead in the duct work. A visual inspection would be in order to check for any breach in the duct system. A duct pressure test would be able to tell you how much air is leaking from the system over all. A hole large enough for an animal to enter would loses a great deal of air, over 300 CFM. It would be worth looking into having this test done and it should cost around $200. Cleaning the air handler and evaporator coil will greatly improve the performance of the air conditioner. Dirt and dust on the evaporator acts as insulation and reduces the amount of cooling done be the coil. Any quality duct cleaning should include cleaning the air handler and coil, and the tech should allow you to watch him perform the work as it is done.
Clean air delivery rate is the amount of clean air an air cleaner provides to a room or space. When determining CADR, the amount of airflow in a space is taken into account. For example, an air cleaner with a flow rate of 100 cfm (cubic feet per minute) and an efficiency of 50% has a CADR of 50 cfm. Along with CADR, filtration performance is very important when it comes to the air in our indoor environment. Filter performance depends on the size of the particle or fiber, the filter packing density and depth and also the air flow rate.[30]

Had our ducts cleaned late April, 2016. Sodium Chlorite was sprayed into ducts after cleaning. Ever since, we have been bothered with eye and nasal passage irritation because of a “chemical” and “musty” odor. This odor is present whether or not a/c is on.) We are told the sodium chlorite (“EnviroCon, manufactured by Bio-Cide International) is used in hospital and nursing home settings and is not hazardous to health. The air duct company’s suggestion is that they come out and spray even more sodium chlorite…we absolutely don’t want this done! Have had various other recommendations about what we need to have done to remedy our problem. We will be unable to stay in our home if a resolution cannot be found. We’d be willing to replace the ductwork if necessary. (One professional suggested that the cleaning may have “knocked something loose” inside the ductwork and that is the source of the irritant.) This home was built in 1920…no idea when the present ductwork was installed. Any suggestions would be appreciated.


As you can see, if we know what the contractor is actually paying for specific equipment, we know what their labor rates are, and we know what they bid the project for, then we can also use some basic algebra (or just let the program do it for us because we’re lazy) to figure out how much of a profit they are making off of us (you) at different bid prices:
Before you choose any duct cleaning service provider, interview as many service providers as you can. Ensure that the service provider is certified by the National Air Duct Cleaners Association or NADCA. Make sure that they hold a good standing in the Better Business Bureau and have all the necessary certifications and license. Be clear about their terms of service. Make sure they have the right equipment to do the job. It is best to go for a company that has been tried and tested successfully by any of your acquaintances or opt for a service provider that has been in the business for quite some time.
All these pro duct cleaners answer with "it's common sense, everything operates better when cleaner" etc. But your explanation is correct. Especially so with flex tube ducting where dust gets "stuck" between the lowest valleys (between wire coil supports) where air flow is drastically reduced -- which is more than 50 pct of the entire interior surface area of the flex ducting. That sounds like a bad thing but also has a good effect of trapping dust from escaping.
Your HVAC unit and air ducts deliver heated or cooled air throughout your home year-in and year-out. The air your HVAC unit produces travels through your ductwork and heats or cools your home via the air vents in each room. The dust and other particles in your home’s air are known as particulate matter, which the EPA defines as "a complex mixture of extremely small particles and liquid droplets." The EPA also notes that "particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles." Having clean air ducts means fewer of these particles moving through your home. If you remove your furnace filter and hold it up to the light, you can probably see several hundred of these minuscule particles floating in the air. 
Air conditioner size is measured in “tons.” However, the tonnage of an HVAC unit is not actually based on its weight. A “ton” is simply a measure of an air conditioner’s ability to cool your home. One ton is the ability of your air conditioning system to cool 12,000 BTUs (BTU stands for British Thermal Unit) in an hour. Likewise, a “2-ton” central air conditioner is able to cool 24,000 BTUs per hour.
I to had an odd layer of white'ish dust building up especially during seasonal periods when the HVAC ran a a lot. I carefully swept up the fine dust into a small pile and had it analyzed. Turns out it was very fine fiberglass powder dust. It turns out it is the insulation form the attic! (My attic has blown in insulation). Turns out if you (I) had small gaps around my HVAC registers in the ceiling whee the airs blows into the room. What occurred in my case was that the exiting air at that seam creates a vacuum effect at the grate vent cover and draws and then blows fine insulation dust from the attic into the house. Removing each register grate and sealing each tin outlet gap with calking between the dry wall ceiling and tin fixed the issue. A couple were so bad with bowed gaps I had to screw down the bowed tin to the attaching stud better. Checking the very same glass top desk that catches and shows any dust accumulation now shows only very small amounts of normal house dust build up over several weeks. A big, big improvement. You might have a look by simply removing a couple vent covers yourself.
In the United States, HVAC engineers generally are members of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), EPA Universal CFC certified (for installation and service of CFC HVAC devices), or locally engineer certified such as a Special to Chief Boilers License issued by the state or, in some jurisdictions, the city. ASHRAE is an international technical society for all individuals and organizations interested in HVAC. The Society, organized into regions, chapters, and student branches, allows exchange of HVAC knowledge and experiences for the benefit of the field's practitioners and the public. ASHRAE provides many opportunities to participate in the development of new knowledge via, for example, research and its many technical committees. These committees typically meet twice per year at the ASHRAE Annual and Winter Meetings. A popular product show, the AHR Expo, is held in conjunction with each winter meeting. The Society has approximately 50,000 members and has headquarters in Atlanta, Georgia.
If there is stuff in the ducts, the fact that it’s laying there and not being blown into the rooms is proof positive that it is hurting no-one. The 5-6 exceptions you cite in this article I’ll buy, but only with the caveat that at least some of those could have been avoided by proper protection (during remodeling for example) – and if asbestos/lead/whatever winds up in your ducts- the remodeling contractor should be the one paying to remove it.
What you might not know is that the brand you choose is one of the most important factors in determining a fair HVAC installation cost. So, before delving in-depth, let’s take a quick look at the average prices of a new air conditioner and matching coil by brand…keep in mind, these are the average prices (by brand) that contractors pay for your AC equipment, and it is meant to give you a rough guideline until you are closer to buying:

Be careful of dishonest HVAC contractors. There’s no magical formula to see if an HVAC contractor is scamming you, unfortunately, but remember that they typically do this in one of two ways: first, they are charging grossly low prices (far below everyone else), or second, they aren’t including what everyone else is. In the first situation, they will charge you change fees, other hidden fees, or they stole the equipment and are passing themselves off as legitimate contractors (very common in California these days). In the second situation, they are charging you a very fair price, but aren’t including what the other contractors are (i.e. charging $10,500 for the installation which is fair, but not including the ductwork which is a scam unless there is some other, complex stuff going on there).
He proceeded to clean each heat register by removing the grille and blasting it with an air pressure hose toward the duct opening thinking that the dust would magically be sucked inside. In one room this caused a ceiling smoke detector to go off because the excess dust fooled it into thinking there was smoke. I put my hand in front of a register he wasn’t working on and could hardly feel a suction. Although we discussed how I open and close damper doors, I realized later that he never checked, opened or adjusted them during the cleaning. He could have closed all but the one he was working on in order to increase suction results. His next step was to blast air into the duct and then attach a “squid-like” device that slapped around inside the duct as far as he could reach. This is important! In a newer house, ducts have long straight runs from the furnace. In older houses like mine they can turn and twist. In fact, the duct we have a problem with runs straight up from the basement inside a wall and turns 90 degrees into a soffit for three feet then into two 90 degree turns to get into the floor joist area for another two feet and finally a 90 degree turn up to the second floor register. When he cleaned this one he could only get three feet into the register with the hose or squid because of the turns. That was the case with most. Hardly what could be described as a decent cleaning.
Air duct cleaning service providers may tell you that they need to apply chemical biocide to the inside of your ducts as a means to kill bacteria (germs) and fungi (mold) and prevent future biological growth. They may also propose the application of a "sealant" to prevent dust and dirt particles from being released into the air or to seal air leaks. You should fully understand the pros and cons of permitting application of chemical biocides or sealants. While the targeted use of chemical biocides and sealants may be appropriate under specific circumstances, research has not demonstrated their effectiveness in duct cleaning or their potential adverse health effects. No chemical biocides are currently registered by EPA for use in internally-insulated air duct systems (see Should chemical biocides be applied to the inside of air ducts?).
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