How Does Duct Cleaning Work Step by Step, Furnace Included

The principle: source removal

NADCA, the duct cleaning trade association, calls the method source removal. Two things happen at once. A powerful vacuum holds the system under continuous negative pressure so that loosened dust is drawn toward the collection hose instead of drifting into the rooms, and agitation tools break the dust free from the inside surfaces of the ducts. NADCA lists brushes, air whips, compressed air nozzles and so-called skipper balls as agitation devices, along with hand brushing and contact vacuuming. Without both halves the job does not work: suction alone leaves stuck dust behind, and agitation without suction blows it into the house.

Step one: look before anything is opened

A sound job starts with an inspection of the furnace, the coil, the main trunks and a sample of branch runs, ideally with a camera so the homeowner can see what is there. The EPA also says the service provider should check for asbestos in the system before cleaning, which matters in older houses. This is also the moment to agree on scope and price. In Illinois, the Home Repair and Remodeling Act requires a written contract or work order with the total cost before home repair work over $1,000 begins.

Step two: connect the vacuum and protect the house

The vacuum may be truck-mounted or portable; NADCA says either can be used to contain the dust. The EPA says vacuums that exhaust indoors should use HEPA filtration, and that carpets and furnishings should be protected. The vacuum is usually connected to the main supply or return trunk near the furnace, and registers are covered so the suction concentrates on the ducts being cleaned.

Step three: open access points

Technicians use existing openings such as registers, grilles and service panels wherever they can. Sometimes they need to cut access holes in the ductwork to reach inside. NADCA notes that making and closing those openings takes real skill, and the EPA says any holes cut should be sealed and insulated again afterward. Ask where holes will go and how they will be closed.

Step four: agitate run by run

With suction pulling, each supply branch and return is worked with brushes or whips until the inside surfaces are clean. Flexible duct and fiberglass-lined duct need gentler tools than bare metal; the EPA recommends soft-bristled brushes for fiberglass to avoid tearing it. Returns matter as much as supplies, because they carry the household's dust back to the furnace.

Step five: clean the equipment, not just the ducts

NADCA recommends cleaning the entire system: ducts, registers and grilles, the plenum, the coil, the drain pan, the heat exchanger, the air cleaner and the blower motor and assembly. In a Schaumburg house that last item deserves particular attention. O'Hare averages close to six thousand heating degree days a year, so the furnace blower moves air through the house for most of the cold season, and its wheel collects dust faster than most duct runs. Pulling and cleaning that wheel is a job of its own, covered in furnace blower cleaning.

Step six: chemicals only after cleaning, if at all

NADCA says antimicrobial products should be considered only after mechanical cleaning and only if registered with the EPA. The EPA adds that no biocides are registered for fiberglass duct board or fiberglass-lined ducts. A cleaning does not need a spray to be complete.

Step seven: close up and check

Access holes get patched and sealed, registers go back, a fresh filter goes in, and the system is run to confirm it heats and cools normally. The EPA's checklist says every cleaned surface should be free of debris you can see, the coil should be clean, and the drain pan should drain. Before-and-after photos from inside the same runs are the easiest proof.

What varies in Schaumburg houses

Much of the village was built between 1960 and 1990, so duct systems are often decades old, with basement trunks that may have been patched or extended over the years. In a Weathersfield house that started with hot-water heat, ducts may have been added later for central air, which changes where the runs go. Leaky joints found during the inspection are a separate repair, and Nicor Gas's 2026 program offers a duct sealing rebate through approved contractors. Typical costs for the full process, and for a cleaning after a remodel through post-renovation duct cleaning, are listed with sources on the pricing page.