I have lots of my auditing customers who ask me about duct cleaning, and if they should do it.  It seems like the only way to get them really clean is with some sort of roto brush, but it also seems like that process is going to possibly do more damage than good.  Obviously this really depends on the duct system and the quality of the craftsmanship, but I was just looking for the Pro's opinions.  Thanks!

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I've never found any studies that say that duct cleaning has been shown to save energy or improve health or provide any benefit. Cleaning and servicing the blower fan will save energy, cleaning the ducts as an energy measure won't. If it was such a great measure there would be utility rebates for it, and there aren't.

A study by the EPA a number of years ago found that duct cleaning decreased air quality drastically in homes after they were cleaned because all the materials that had adhered to the ducts were being blown around the house after they were cleaned. If you think about it, particles stuck inside your ducts are not being blown around your house, cleaning them loosens up all that stuff, that can now be blown around your house if it isn't all removed by HEPA vacuuming. Your ducts may be functioning better as a air filter than your air filter is or there wouldn't be anything stuck to them in the first place.

From the EPA's website:

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 or go down after cleaning. This is because much of the dirt that may accumulate inside 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 health.

EPA does not recommend that air ducts be cleaned except on an as-needed basis because of the continuing uncertainty about the benefits of duct cleaning under most circumstances. EPA does, however, recommend that if you have a fuel burning furnace, stove, or fireplace, they be inspected for proper functioning and serviced before each heating season to protect against carbon monoxide poisoning. Some research also suggests that cleaning dirty cooling coils, fans and heat exchangers can improve the efficiency of heating and cooling systems. However, little evidence exists to indicate that simply cleaning the duct system will increase your system's efficiency.

This says it all

Ed Minch

I definitely defer to Ed's expertise as to whether there is any energy efficiency benefit from duct cleaning. It makes sense to me that simply cleaning the dust out of your ducts wouldn't do much, if anything, to improve your system's performance. I would think your ducts would have to be severely restricted to the point where it is restricting air flow before it starts affecting performance, and I can't imagine how they could get that bad.

But I would submit one potential situation in which duct cleaning might be beneficial - not from a health or energy savings standpoint, though: odor.

When we bought our current house, as soon as we started preparing to move in, it became obvious that the previous owners had had a dog, and that they must have had a bunch of air fresheners or something in the house when we had done the walk-throughs. The dog certainly never was there any time we had visited the house, and we had not detected any doggy smell, but after we took possession, we could smell a definite doggy smell, and we kept finding lots of long dog hair everywhere.  

Even after lots of cleaning, after a week or two of living in the house, we couldn't stand the musty, doggy smell anymore, so we finally hired a duct-cleaning service. They found a surprisng amount of crud in the ducts - dog hair everywhere, and in one case (a duct under a floor register), a pile of dry dog food in the duct!

When I came home from work in the evening on the day they had done the cleaning, the difference was immediately noticable. The entire house smelled fresh and clean, where before it had that wet doggy smell - and we don't even have a dog.

Ours might be an extreme or special case, though. But in our case, the duct cleaning definitely provided that benefit. I seroiusly doubt it provided any other benefit, in terms of health or energy efficiency. But it was worth it for us, to make the house smell better. If not for that doggy odor, we never would have bothered getting the ducts cleaned.

The duct cleaning definitely took care of the odor and it has been a permanent solution. After five years, the odor still is completely gone.

That makes sense, I was also thinking if there had been any kind of rodent infestation, that might be another reason to have them cleaned.  Thanks.


We had a similar experience to Mr. Taggart, except that the problem was a musty smell which aggravated allergies.

The house is over 100 years old and has previously had a coal burning furnace, an oil burning furnace and most recently a natural gas furnace. When I reached my hand down into the duct work (to make sure there was actually metal duct work, not just air flowing through a joist space), it came away with a greasy black film - years of coal and oil residue.

We got the ducts cleaned and then also replaced the 60 year old natural gas furnace, installed a Honeywell Electronic Filter and sealed all the ducts (in that order). The musty smell has disappeared and our allergies are much better. I don't think the duct cleaning will improve our energy efficiency, but it has improved our interior air quality and health. 

Energy - seems like a real risk that the methods of duct cleaning (at least a "rotor" approach like Gordon mentions) truly risk making leaks worse, or being the final straw in the failure of tape, etc.


Odor - I just encountered some ducts that had been breached by rodents.  Once the ducts become a potty, I suspect the odor is particularly difficult to eliminate.

Based on the results of my own duct cleaning that was done by a highly competent and meticulous team I would strongly recommend the service in older houses, houses with pets, and houses where occupants have respiratory issues.

My house was build in 1928 and was originally heated by a coal fired gravity furnace. Nobody ever thought to clean the ducts. The cleaning by a skilled and knowledgeable team yielded almost a garbage can full of crud, coal dust, generic dust, dust bunnies, dust elephants, papers, Christmas tree needles, small kids' toys, animal fir, cigarette butts, anything that 80 years worth of cats could knock down a cold air return, and one mummified mouse.

I then installed a Photronic air cleaner with a MERV 11 pleated media filter, an electrostatic collector, and UV lights (the jury is out on whether the lights were a worthwhile investment). By vacuuming out the cold air returns and floor registers periodically and generally keeping an eye on things, the ducts may not have to be cleaned again for another 80 years.

I suspect that routine maintenance by homeowners could postpone the need for cleaning for a good long time, that cleaning ducts in newer homes is not worth it unless there are unusual circumstances, and that there is no such thing as a $199 duct cleaning.

The guys who did my house spent a full day with a custom system that they built themselves. Thanks, Herb.And, yes, I did feel sorry for the mouse.

My coments of 10 days ago still stand.  Note that the EPA says

 "EPA does not recommend that air ducts be cleaned except on an as-needed basis because of the continuing uncertainty about the benefits of duct cleaning under most circumstances."  

and that there are certainly times when ducts should be cleaned.  They are not talking just energy, but the need to clean ducts at all.  The fact that your 83 old ducts had all that stuff in them means that the stuff was not in the air.  The only time cleaning would be critical is when the stuff in the ducts got thick enough to affect the air flow.  

Here is something that I have witnessed/noticed twice in 31 years: When doing duct analysis I turn on the system fan to the air conditioning speed in the spring.  All winter the lower fan speed has been in effect and a certain amount of stuff has fallen out of the duct stream at that speed.  The faster speed makes a little puff of dust come out of the register just once - then no more.

So stuff that has accumulated in the ducts wants to stay there, and if there is no moisture in the ducts to make things grow - the usual case - then there is no need to clean the ducts.

But people have to make themselves comfortable.

Ed Minch




Forget the ducts. Dig deeper and get to your evaporator coils (or indoor coils if you like). WHY?  


Beautiful shinny fins on the top of the A-coil are hiding a monster within! Even when scoped by a camera in the duct usually they view only from the supply side of the duct as that is accessible. Inspection truly must be done either by lifting the coil up OR by pulling the blower to look up past heat exchanger OR by opening the side of the coil (professionally).


I have found a shiny coil from above to have globs of mold/algae clinging below. The clean up required a 1" wide wire brush that I had to hose off after EVERY down stroke thru the fins as it was too gummed up to stroke again.


The above house had had the ducts cleaned just a few years before had no pets, no smokers, and were really non-cookers. Prior owners had pets and it was still covering the coils causing a really groovy wet environment.


Strong possible health issue.


The a/c's superheat had been tuned to the prior low airflow on high in cooling. Loss of efficiency there. Severe dollars wasted in the Atlanta sun.


So, back to my thought, ducts are just a hint of what may be lurking behind the shinny door (coils). If the ducts are dirty then cleaning them is not enough and the coil will reflect the duct. Moist coils are glue and winter heat doesn't remove the buildup.


Happy Thanksgiving! 



The reason coil cleaning doesn't get done is because it's labor intensive, therefore expensive for homeowners to have done. In an effort to increase SEER ratings and make them in compact sizes coils have more fins per inch and more "coil rows", increasing face velocity and static pressures. Making coils "the old way" with less rows, more surface area and less fins per inch decreases initial SEER rating, but after the coil has been in service for 5 years actually has a higher real world SEER rating than the newer coils do after the same 5 years worth of dirt/dust accumulation.

IMHO the best "preventative medicine" for most homeowners is to have the 4" filters installed, they capture MUCH more gunk than the standard 1" models.

Bob   4 inch filters are not a better filter, they have more surface area and last longer.  If you look the the MERV rating of the 4 in filters they are in the range of an 8 or 10. That is mid level filtering.

Furnace filters are a balance of filtering and air flow. The more filtering the less air flow.  Air flow is measured in static pressure. The better the filter the higher the static pressure which equate to lower air flow. This will result in a decrease in efficiency. 

Duct cleaning is not a waste of money at all. It is a return of money in the shape of good health. So it is so important to maintain it in good condition.


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