Air duct cleaning is one of the easiest HVAC services to sell and one of the easiest to overbuy. In Menlo Park, Atherton and Portola Valley it pays off in a handful of specific situations and does little in the rest. Here is how to tell which one you are in, what a proper cleaning involves, and what to look at before you pay for one.
When cleaning is worth it
- Debris comes out of the registers when the fan starts: insulation fibers, drywall dust, bits of leaves.
- Rodents or insects have been in the ducts. Crawlspace ducts under older ranch homes are a common nesting spot. Once the entry point is sealed, the affected runs are cleaned and, with your agreement, sanitized.
- After a remodel that sanded drywall or refinished floors while the system was running.
- Visible growth on hard duct surfaces or around the coil, once the moisture behind it has been found and fixed. Cleaning without fixing the moisture only resets the clock.
- You are moving into a house with no service history and the inspection shows heavy buildup in the trunks.
When it usually isn’t
- Gray dust on the register grilles. Wipe them. A light film inside a duct is normal and stays put.
- Dust on furniture. Most of it is made inside the house or blows in through doors and windows.
- Spring pollen in the foothills. In Portola Valley and Ladera, pollen arrives every season through doors, windows and leaks. A deeper filter and a shorter change schedule deal with it; cleaning the ducts does not stop it coming back.
- A few smoke days. Replace the filter first. If a smoky odor still comes from the vents weeks after the air has cleared, that is the time to inspect the ducts.
- Leaking ducts. If a return is split open in the attic, it will be dirty again within months. Fix it first with duct repair.
Dirt or leak? Check before you clean
Dark streaks at the edges of supply registers, a dusty attic smell when the system starts, and a filter that goes gray in a few weeks often point to a leak rather than to dirty ducts. A return split at a joint in the attic or crawlspace pulls dust and loose insulation in behind the filter. That gets looked for during the pre-cleaning inspection, because cleaning ducts that are about to be resealed or replaced is paying twice.
What a proper cleaning involves
- Inspection and photos. Registers come off; the accessible runs, the return plenum and the blower compartment are checked and photographed so you can see the starting point.
- Containment. The duct system is put under negative pressure with a filtered vacuum connected to the trunk, so loosened dust is pulled out of the house rather than pushed into it. Registers are covered while each section is worked.
- Agitation matched to the duct. Brushes, air whips or compressed-air tools loosen what is stuck to the walls. Sheet metal tolerates more than flex duct or duct board, and the tool is chosen accordingly.
- Registers and grilles are removed, cleaned and refitted.
- After inspection. The same spots are checked and photographed again.
Ask whether the blower wheel and the indoor coil are part of the job. Clean ducts feeding a dirty blower do not stay clean for long; that work is often done during a furnace tune-up or AC tune-up.
Sanitizers and coatings
Sprays and coatings are not part of a routine cleaning. They make sense after a rodent problem, or after growth has been removed and its moisture source fixed, and only when you agree to them. Ask what the product is and whether its label permits use inside HVAC ducts. A coating sold to “seal in” dust or loose fibers is no substitute for repairing or replacing damaged duct.
Older ducts, zoned homes and the price
Most cleanings take 2 to 4 hours and cost $299 to $599. The number of systems and supply runs, attic and crawlspace access, and the duct material move the price. Large homes in Atherton with two or more systems, or one system split into zones, have more trunks and registers to cover and sit toward the top of the range. Zone dampers are opened for the cleaning and checked afterward, so every zone still gets its air.
Old ductwork deserves a frank look before anyone cleans it. Mid-century houses in Menlo Park often have original sheet-metal ducts with dried-out tape at the joints, or flex duct from a later remodel that has gone brittle in the attic heat. If the inspection finds crushed, torn or disconnected runs, the written estimate says so, and repair or replacement may be the better place for the money.
Before you book
Note where debris or odor shows up, any signs of rodents, and when the last remodel happened. Photos of the registers, the filter and the attic or crawlspace access help the first visit. For what failing ductwork looks like, see signs your ductwork needs attention; if your concern is the air itself rather than the ducts, start with an indoor air quality check.