Supply, return
and the parts between.

Property context in Saratoga

California’s energy code can require HERS field verification and diagnostic testing on heating and cooling work. The California Energy Commission says that, depending on the work being done, HERS testing may be mandatory, and that properly permitted work will trigger any necessary HERS testing. It adds that a contractor should be able to explain permitting requirements to the homeowner and that HERS testing should be part of that discussion, and that a rater should identify themselves with a photo badge. Ask early whether the proposed work is a duct or equipment alteration that needs a permit, because cleaning and replacement are not the same scope. Confirm the permit position with the City of Saratoga.

The US Environmental Protection Agency does not recommend that air ducts be cleaned routinely, but only as needed, and lists the conditions that would justify it: substantial visible mould inside hard-surface ducts or system components, ducts infested with vermin such as rodents or insects, and ducts clogged with excessive dust and debris that is released into the home. EPA also says no chemical biocides are currently registered for use in internally insulated air duct systems, and that sealants are not recommended for routine use. Ask to be shown the condition before agreeing to a scope. EPA guidance describes when cleaning may be appropriate; it is not a diagnosis of your system.

Area-wide context is not a finding about your own property.