North Bay Mold Remediation connects Marin and Sonoma property owners with local mold contractors who handle mold in furnaces, air handlers, and ductwork, working alongside an HVAC contractor where the job calls for one.
How mold gets into an HVAC system
Ducts don't grow mold on their own. Something has to be wet. In North Bay homes the usual causes are an air conditioner coil and drain pan that don't drain properly, ducts and furnaces in a damp crawl space or attic, condensation on uninsulated ducts, a roof or plumbing leak onto ductwork, and flood water reaching floor registers or under-floor ducts. In raised-floor homes the ducts often run through the crawl space, so a wet crawl space and duct mold can go together. See crawl space mold remediation.
The EPA's guidance on mold in ducts makes the same point it makes everywhere else: if the conditions that caused the growth are not corrected, the mold comes back.
What EPA and NADCA guidance says
- Routine duct cleaning isn't recommended. The EPA advises cleaning only as needed, and lists substantial visible mold inside hard-surface ducts as one reason to consider it.
- Ask to see it. Much of a duct system is out of sight. The EPA suggests asking the provider to show you any mold they find, and notes that lab analysis may be needed to confirm a substance is mold.
- Sheet metal can be cleaned; fiberglass usually can't. Bare metal ducts can be cleaned. Wet or moldy duct liner, duct board, and insulation are normally replaced, a step EPA, NADCA, and NAIMA all recommend.
- Go easy on chemicals. The EPA says no biocides are registered for internally insulated ducts, and sealants should never cover wet liner or active mold.
- Check the cleaner. The EPA suggests confirming that a duct cleaner follows NADCA's air duct cleaning standards, and NAIMA guidance for fiberglass ducts. EPA does not certify duct cleaning companies, and it advises avoiding providers who make sweeping health claims.
Who does what
HVAC mold jobs often take two trades. A mold remediation contractor contains the area, removes and cleans moldy materials, and handles any crawl space or attic growth around the equipment. Work on the furnace, coil, drain lines, and duct replacement typically falls to an HVAC contractor. In California that is the CSLB C-20 Warm-Air Heating, Ventilating and Air-Conditioning classification. One firm may hold both kinds of license or subcontract part of the job; just confirm who is responsible for each part in writing, and check licenses at cslb.ca.gov.
In homes built before 1980, old duct wrap and some duct insulation can contain asbestos. Testing may be needed before it is disturbed, and asbestos work needs a contractor with CSLB asbestos certification or a C-22 license plus DOSH registration.
What the job usually involves
- Shutting the system down while it is assessed, and finding the moisture source
- Inspecting the air handler, coil, drain pan, blower, and the ducts that can be reached
- Replacing moldy flex duct, duct board, or lined sections
- Cleaning sheet metal ducts and components to NADCA standards
- Fixing drainage, insulation, or leaks so condensation stops
- Replacing filters and, ideally, an independent check before the system runs normally. See clearance testing.
Local conditions that matter
Ducts in a raised-floor crawl space sit in the dampest part of many older homes, and the Ross Valley's wet winters in Kentfield, Larkspur, and San Anselmo keep those spaces wet for months. In Sonoma County, homes in Guerneville that took on water in the February 2019 Russian River flood, which damaged about 1,900 homes, may have had under-floor ducts submerged. In warmer inland towns like Santa Rosa, summer air conditioning means coils and drain pans handle more condensation, so a clogged drain line matters more. If the smell follows a leak or flood, see mold after water damage.
If you notice a musty odor but haven't confirmed the HVAC system is the source, our musty smell and hidden mold page covers the other common culprits.
Smell mold when the heat comes on? Call (415) 234-5586 or request an estimate and we'll connect you with a local mold contractor.
Mold remediation in Marin & Sonoma
- Mold Remediation → Containment, removal, and cleanup of mold growth in homes and rentals, following the IICRC S520 approach, with the moisture source fixed first.
- Mold Removal & Black Mold Removal → Removing visible mold, including dark-colored growth people call black mold, from walls, ceilings, framing, and contents.
- Mold Inspection & Testing → Visual inspection, moisture mapping, and air or surface sampling to find hidden mold and its water source.
- Mold Clearance Testing → Independent post-remediation testing that confirms the job is done before walls close up or tenants move back in.
- Crawl Space Mold Remediation → Mold on joists, subfloor, and sill plates under raised-floor homes, plus the drainage and vapor fixes that keep it from returning.
- Attic Mold Remediation → Mold on roof sheathing and rafters from leaks, bath fans venting into the attic, and poor ventilation.
- Mold After Water Damage or Flooding → Drying, tear-out, and mold remediation after leaks, burst pipes, and Russian River and creek flooding.
- Bathroom Mold Removal → Mold in shower walls, behind tile, under floors, and on ceilings from leaks and bathrooms without working fans.
- Wall & Drywall Mold Removal → Cutting out and replacing moldy drywall and insulation, and finding the leak or condensation behind it.
- Musty Smell & Hidden Mold Investigation → Tracking down the source of a musty odor when no mold is visible, from wall cavities to crawl spaces and ducts.
- HVAC & Duct Mold → Mold in furnace cabinets, air handlers, and ductwork, coordinated with an HVAC contractor where equipment work is needed.
- Plumbing Leak & Under-Sink Mold → Mold from slow leaks under sinks, behind dishwashers and toilets, and around water heaters and washing machines.
- Rental Mold Inspection & Remediation → Mold in rentals for landlords and tenants: visible mold as a substandard condition under state law, code enforcement, and documentation.
- Home Sale Mold Inspection → Mold inspections during escrow, since termite reports exclude mold, plus remediation before listing or closing.
- Commercial Mold Remediation → Mold remediation for offices, retail, multi-unit buildings, and property managers, scheduled around tenants and operations.
- Mold Air Quality Testing → Air sampling and ERMI-style dust testing, what the lab report can and cannot tell you, and when testing is worth paying for.
Frequently asked questions
Should I have my ducts cleaned because of mold?
Only if there is a real problem. The EPA does not recommend routine duct cleaning, but it does say to consider cleaning if there is substantial visible mold growth inside hard-surface (sheet metal) ducts. Ask the provider to show you the mold they find, since much of a duct system cannot be seen without access.
Can moldy duct insulation or flex duct be cleaned?
Usually not. The EPA says wet or moldy insulation cannot be effectively cleaned and should be removed and replaced, and that once fiberglass duct liner is contaminated with mold, cleaning is not enough to prevent regrowth. EPA, NADCA, and NAIMA all recommend replacing wet or moldy fiberglass duct material.
Is spraying a biocide or sealant inside the ducts a good idea?
Be cautious. The EPA says no chemical biocides are currently registered for use in internally insulated duct systems, and that sealants should never be used on wet duct liner or to cover actively growing mold. Ask exactly what product is proposed and why.
Should I keep running the heat while I wait?
The EPA advises not running an HVAC system you know or suspect is contaminated with mold, because it can spread spores through the building. Ask the contractor about running it once the source is dealt with.
Request a Mold Remediation Estimate
Free to request, no obligation. We'll call you back to talk it through.
Request received
Thanks. We'll call you back soon.