Air Duct Cleaning in South San Francisco, CA

Frequently Asked Questions

1. We run the furnace most of the year but never AC — does that mean our ducts stay cleaner?

   No, it usually means the opposite of what people expect. A heating-only system still pulls household air through the returns every cycle, and South San Francisco's long cool season means the furnace runs across much of the year rather than in a short burst. What actually accumulates here is fine, dark particulate: diesel soot and road dust off the freight routes, plus exhaust drifting in from the 101 corridor and SFO. It's lighter and greasier than agricultural dust, so it films the inside of sheet metal and clings to register faces instead of piling up. You'll often see it as a gray halo on the ceiling or wall around a supply vent.

2. Our crawlspace always smells damp. Is that connected to the ducts?

   Often, yes. The marine air that comes through the gap keeps crawlspaces under the older Old Town and downtown cottages humid most of the year, and ducts running through that space sit cold. Moisture condenses on the outside of the metal and at the boot joints where the duct meets the floor register, and that's where microbial film takes hold. If the duct insulation is old or the joints are loose, that damp smell gets pulled into the airstream and distributed. We check the exterior condition and the boot seals, not just the inside of the runs, because cleaning the interior of a duct that's sweating on the outside doesn't solve the odor.

3. What usually goes wrong with ducts in the older raised-foundation houses here?

   The common pattern is a partial forced-air retrofit grafted onto a house that was originally heated by wall heaters. The ductwork was added later, often routed through a crawlspace that wasn't designed for it, and the runs are short, improvised, and sometimes sealed with tape that has long since let go. We find disconnected sections dumping warm air under the floor, crushed flex, and boots that were never properly fastened to the subfloor. In the 1950s–60s hillside tracts in Sunshine Gardens, Buri Buri and Westborough the issues differ: split-levels and slab construction push ducts into attics, where the problems are more about insulation failures and rodent entry than crawlspace damp.

4. What makes one South San Francisco house cost more than another?

   Access and system layout drive it more than square footage. A 1950s hillside home with a straightforward attic trunk and a clear count of registers is simple work. An older downtown flat on a raised foundation, where the duct system was retrofitted piecemeal into a tight crawlspace with low clearance, takes considerably longer for the same number of vents. Split-levels that split the duct run between an attic and a crawlspace mean two separate access setups. If we find disconnected sections or heavy microbial film at the boots, repair or sealing is a separate conversation from cleaning, and we'll show you what we found before anything gets added.