Air duct cleaning removes built-up dust and debris from the supply and return ducts, registers, grilles and blower compartment of a forced-air system. For homes in Daly City and the rest of our area, the honest rule is simple: it pays off after construction or renovation, after pests, or when contamination is visible or documented. It is not a yearly habit most systems need, and it does not replace a good filter or sealed ducts.
How the job is done
- Look first. We check inside the ducts through registers and access points, and at the blower, so you see what is in there before paying to remove it.
- Put the system under suction. Powerful vacuum equipment connects to the duct system, so loosened debris is pulled toward the collector instead of into the rooms.
- Agitate each run. Brushes and air whips work through the supply and return runs to break debris loose.
- Clean registers, grilles and accessible parts. Registers and grilles come off and are washed; the blower compartment and other accessible components are cleaned.
- Finish with a new filter. The system runs afterwards so airflow can be checked at the registers.
Most jobs take 2 to 5 hours, depending on how many runs there are and how easy they are to reach.
When it is worth doing
| Situation | What to look for | What else to fix |
|---|---|---|
| After construction | Drywall dust and sawdust in registers and returns | Next time, seal the returns and switch the system off while work makes dust |
| After renovation | Fine dust puffing from registers when the blower starts | Change the filter; check the blower wheel and coil |
| Visible mold in ducts | Growth on duct surfaces, not just grey dust | Find and stop the moisture source first |
| Pests | Droppings, nesting material, a smell near registers | Seal entry points; replace chewed or soiled flex duct |
| Years of neglect by a previous owner | A missing filter, matted debris at the returns | A filter that fits and a closed filter slot |
If you are buying a home, the HVAC part of the inspection is the moment to find the last two; our guide to the HVAC side of a home sale lists what to look at.
When it isn’t the answer
- Dust on furniture. On its own, it is not a sign the ducts are dirty.
- A musty smell from a damp house. Cleaning won’t help when the moisture is in the rooms; that is a humidity problem.
- Weak airflow to one room. That is usually a leak, a crushed run or a disconnected boot, which ductwork repair fixes.
- Routine yearly upkeep on a system with a good filter and sealed ducts.
Ducts in the garage: clean, then seal
Many mid-century Daly City homes have the furnace in a ground-floor garage, with the return duct running through it. A leak in that return, or a missing cover on the filter slot, pulls garage air into the system: dust, fumes from stored paint and solvents, and exhaust from a car warming up. Cleaning does not stop that; duct sealing does. When a return in the garage or a crawlspace has been drawing in dirt for years, cleaning and sealing belong together. A carbon monoxide alarm on the floor above an attached garage is a must either way.
Duct materials need different handling
Bare sheet metal stands up to brushing. Flex duct (the round, plastic-jacketed kind) and fiberglass duct board or lined ducts can tear or shed fibers under aggressive brushing, so they are cleaned gently or, when moldy or damaged by rodents, replaced. In homes from the 1940s to 60s, look at the old duct wrap and tape before anyone works on them: some older materials contain asbestos and should be tested before they are disturbed.
Questions to ask any duct cleaner
- Will you show me the inside of the ducts before and after?
- Are the returns and the blower compartment included, or only the supply registers?
- Is anything sprayed into the ducts, and what is it?
- How is the system kept under suction while the runs are agitated?
Price
Duct cleaning runs $300 to $800 per service. The number of supply and return runs, how easy they are to reach, the amount and type of debris, and whether the blower compartment needs heavy cleaning set where a job falls. You get a written estimate before any work begins, with no hidden fees.