AC installation in Mill Valley is often a first installation rather than a replacement. Many homes here, especially those built from the early 1900s to the 1960s, were designed for heat only, and for years the breezes and the shade of Mount Tamalpais made cooling feel optional. Then a sunny bedroom or a home office starts running hot in the afternoon and the question comes up. The answer depends on what the house already has: ducts or no ducts, a newer furnace or an old one, room for equipment or none to spare.
Three ways to add cooling
Central air on the existing furnace. If the home has a forced-air furnace in reasonable shape and ducts that can carry more air, an indoor coil on the furnace plus an outdoor condenser is the most direct route. Crawlspace ducts need a close look first: cooling moves more air than heating, and uninsulated ducts in a damp crawlspace sweat when cold air runs through them.
A heat pump instead of an AC. If the furnace is old, a heat pump replaces both. It cools in summer and heats the rest of the year, which on shaded lots and north-facing slopes means most of the year, through the same ducts and with one outdoor unit.
Ductless mini-splits. Homes without ducts, or with no space to add them, get cooling and heating room by room from wall-mounted or ceiling units. This is often the cleanest option in older houses; see mini-split installation in Mill Valley.
Sizing for your lot, not your square footage
Two Mill Valley houses of the same size can need very different equipment. One sits under redwoods and stays cool until late afternoon; the other faces southwest on an open hillside and takes full sun. A Manual J load calculation accounts for that: window area and orientation, shade, insulation and ceiling heights. Getting the size right matters more here than in hot inland towns, because an oversized unit in a mild climate runs short cycles, never dries the air and leaves a damp home feeling clammy.
Placing equipment on steep and wooded lots
Outdoor units need clear airflow and a stable base. On sloped lots we use a level pad or wall brackets, and we keep the unit out from under trees that drop needles and leaf litter onto the coil. We plan the refrigerant line route so it stays within the manufacturer’s length limits and is protected where it runs along the house. Indoor coils and air handlers often go into tight closets, attics or crawlspaces, so we check service clearances before choosing equipment. Older electrical panels sometimes need a new circuit or an upgrade; we check during the visit so it appears in the quote.
How the installation runs
- Consultation: we look at the house and talk through which rooms overheat and what you want to spend.
- Load calculation: Manual J sizing for the home as it really is.
- System selection: options and a detailed, upfront quote. Financing is available with approved credit.
- Installation: to the manufacturer’s specifications, with the permit and paperwork handled for you.
- Testing and walkthrough: we verify airflow, charge and temperature drop, explain the manufacturer’s warranty and show you how to run the system.
For homes near Muir Woods and everywhere else in town, the Mill Valley service area page lists the rest of what we do, and our AC installation page explains equipment types and efficiency in more detail. If you already have an AC that has stopped working, start with AC repair in Mill Valley; if the furnace is due as well, see furnace installation.