By Dan Stradford, Chief Executive Officer
Action Duct Cleaning Co., Inc.
Altadena, CA


Air conditioning and heating contractors often hear about duct cleaning companies offering their services but they may not be certain when a client actually need to get his system cleaned.

Here are a few pointers on what to look for from an old-timer with more than two decades in the duct cleaning business:

Replacing the air handler: Etch this one in stone. When you install a new air handler onto old ductwork, you run the risk of dirt blowing from the ducts. This can get very messy. The problem is simple. The new air handler blows harder. The old fan didn’t disturb the dirt lying in the ducts because it was too weak. You come along and bang on the ductwork while yanking an old unit and hooking up a new, more powerful one. The dirt is now loose and ready to explode from the registers.

We get calls on this with some regularity. Sometimes the customers are pretty mad. Even veteran HVAC contractors get caught doing this sometimes. It doesn’t happen with every changeout but it happens often enough to warrant concern. If in doubt, get the ducts cleaned.

Even changing a simple motor change can cause this. We had one client who had a bad motor replaced in a unit that had gone unused for a year. Dirt blew everywhere. All over the beautiful carpet. All over the grand piano. On the paintings. The insurance company settled for $25,000.

Consider the ducts on your next air handler changeout, especially if there is a visible buildup of dirt in the system.

Bad filters: If you see a bad filter set up of any kind, chances are your client has a fair amount of dirt buildup in his ducts. The problem could range from gaps or holes in the filters to a missing filter to no filters at all. If it’s a short-term matter, such as a filter fell down for a week, there’s no need to worry. But if filters have been missing for some time, one look will tell you the ducts are filthy. They need to be cleaned.

Similarly, air handlers that have been neglected (no service) for a long time commonly are quite dirty.

Mold growth: If you see mold growing in the ducts or air handler, get it cleaned. If you see conditions that promote mold growth such as standing water or wet insulation, fix it. If you don’t and the mold spreads spores into the building, it could be a health hazard and you could have trouble.

The air handlers at one school we serviced got so bad (before we arrived) that the building smelled like fish. Kids were complaining of illness. Parents literally picketed outside with gas masks on – in front of the evening news cameras. Then came the lawsuit.

Fortunately, mold doesn’t normally live in the ductwork itself except in humid climates or where moisture is getting into the ducts. But minimally the air handler should be cleaned when mold growth is evident. If the ducts are dirty or contaminated with mold, they should be included.

Dirty ducts: Here the question is, “How dirty is dirty?” All ducts have some dust residue in them as a natural byproduct of air passing through. But when the dirt begins to pool, that is, you can see “puddles” of it in the ducts, it is starting to get out of hand. If it coats the duct interior 1/16” or more, you should probably consider cleaning.

One Japanese study found that dirt began blowing out after accumulation reached 0.8 millimeter. That’s about 1/32 of an inch.

If you see dirt and lint hanging from the walls of the duct interior, a cleaning was due long ago.

Dirt blowing out: This is one of the most common reasons we are called. There is normally no alternative to duct cleaning in this situation. Usually the system has reached its dirt saturation point and the particles blow and blow. Sometimes this can be caused by a loose duct joint, filter gaps or leaky air handler. But the normal reason is too much dirt in the ducts. Clean ‘em.

Bad smells: This can come from the air handler, the ducts or both. Some places like nightclubs accumulate cigarette smoke, perfume, human sweat, and a host of other stale odors that can saturate the dirt in a duct system until the smell becomes quite distasteful. Cleaning the system gives the building a new lease on life.

Before blaming the ducts, however, be sure bad odors aren’t coming from elsewhere and simply being transported by the ducts.

Sick occupants: With indoor air quality in the news some building occupants blame their physical ailments on the air conditioning system. They may be right. They may not. For some of our clients, a cleaning is worth the cost – whether they need it or not – because it alleviates the liability of being accused of neglect.

We are sometimes asked to test duct systems for microbial growth and sometimes we find it. Cleaning is a positive step in such a case, but this is not always the sole reason people are getting sick. The subject of “sick building syndrome” is a complex one which has to be looked at from more than just one angle.

Allergies, however, can definitely be improved by duct cleaning. Allergens can sit in the ductwork and be blown daily into an area causing discomfort to sensitive individuals.

An air conditioning contractor is often like a doctor. He may see his client’s system in poor physical health or the customer tells him of various symptoms.

Like a physician, a well-informed contractor knows when the remedy needed is duct cleaning. Hopefully, the above guidelines will help him diagnose properly so his clients stay in tip-top shape.