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Duct Cleaning: What You Need to Know

As summer begins, it’s a good time to make sure the ductwork system in your home is in good shape and clean. Except for ‘Direct Vent’ equipment, HVAC systems that work by moving air need ductwork for both supply and return air. A typical residence can have 3 to 5 ‘air changes’ every hour; that’s a lot of air to move.

Before talking about ductwork cleaning and air filters though, we need to start at the beginning and think about the system’s condition and integrity.

  • How old is the system, and what is its history?
  • Have you owned and managed the system since it was installed, so that you know the filtration has not been neglected, properly maintained, or even removed from time-to-time? (it happens)
  • Have you every inspected the ducts inside and out, including a Flow Hood/Airflow ‘pressure’ test to know how sound the ductwork is and if there are leaks or separations? The ’Comfort Institute’ a national trade association publishes that the average ‘leakage’ they see reported over the years is 20% – 30%. That’s average, and that is a huge amount of air, providing a lot of opportunity for both leakage (of warm/cold air and energy) and infiltration (of particulates, vermin debris, mold, mildew etc.).
  • Has there been a remodel since installation/last cleaning?

All of these things need to be considered and properly addressed in order to honestly assess the condition of the ducting on an HVAC System. If the system is physically sound and in good shape, then you can address its maintenance and cleaning.

In an average size residence/unit with normal occupancy, up to 40 pounds of dust and particulate will actually try to go into and through it; that’s a lot of dirt! And that’s why even if the system is in good condition, the Air Filters need to be serviced/changed on a very regular basis.

How often? At the risk of sounding like a smart aleck, the honest answer is this… as often as they need … and every system is different.

  • The number of people that live/work there.
  • Their age and lifestyle and personal hygiene habits.
  • How and what they cook.
  • Any smokers?
  • Do they have any pets?
  • Do they often have visitors?
  • Is laundry done there?
  • Are there bathroom fans that always run during bathing/showering?
  • Are there any issues/smells/problems that have recently developed?
  • Has there recently been a remodel?
  • Is the outside air quality unusually bad? (like smoke, pollution etc.)

All these types of things matter.

As I have mentioned in past articles, dirty filters look dirty, and clean filters look clean. Simply pull the filter out of its holding area in the system and look at it.

  • Does it look relatively clean, like a new one looks?
  • Is there anything visibly built up on it?
  • When you hold it up to a light, can you see through it?
  • Is it in good shape, or is it bent, flimsy or out of shape?

If the filter looks good, it likely is good. usually, we recommend that all filters be replaced every 6 to 12 months, even if it ‘looks’ good. Because regardless of the filter size or thickness, none of them are made real strong structurally, and if they go too long and debris builds up on them, a lot of air resistance is created, and the system air can cause them to ‘flex’ and even to get ‘sucked’ into the ducting partway (or all the way). When that happens they aren’t working at all, because the air will simply scoot right around it instead of going ‘through’ it and getting captured.

Unlike many companies, we do not recommend cleaning the ductwork in an HVAC system annually. Our experience has been that an average system that has been serviced properly and faithfully should consider having the ductwork cleaned every 5 to 15 years; depending on the many variables mentioned above. Proper ductwork cleaning is not a DIY or Maintenance Person project. It takes highly specialized equipment, and should be done by an established, specialized company that uses NATE Certified Technicians, and that has a good track-record and stands behind their work. So again…although duct cleaning isn’t normally needed every year, it is good to consider it regularly.

Ducting is an important component of many HVAC systems. Proper maintenance will ensure that its effect on our comfort, air quality, and health is as good as it can be.


Bruce Davis, Sr.
President, Director of Education and Learning, Sales Manager, Licensed Journeyman Plumber, Licensed Electrician,
HVAC/R Electrical Administrator, HVAC/R, Certified WA State C.E.U. Instructor

Bruce Sr is President of Day & Nite Plumbing & Heating, a 67-year-old family owned and operated plumbing and heating business in Lynnwood, Washington. Bruce can be contacted at: Email: Bruce@dayandnite.net

Day & Nite Plumbing & Heating Inc. 16614 13th Ave. W. Lynnwood, WA 98037 800-972-7000

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