AC installation in Portola Valley has to account for the hillside, larger floor plans, afternoon sun on the glass and an outdoor unit that stays quiet. Before any equipment is chosen, the load, the duct capacity and the electrical supply need checking, along with whether a heat pump or a zoned system would fit the home better than a straight AC swap. Many owners here also ask about heat pumps and furnaces, so this page compares them. The standard replacement is explained on our general AC installation page.
Size for the afternoon, not the old unit
A foothill house that is comfortable at breakfast can overheat by late afternoon in rooms with big west- or south-facing windows, while shaded rooms on the downhill side stay cool. Copying the tonnage of the old unit carries over whatever mistake was made last time. We work from Manual J-style inputs room by room: glass area and direction, insulation, ceiling height, shading from trees and the slope. When one wing overheats and the other does not, zoning or a second system often does better than one larger unit, and the ducts have to carry the airflow either way.
Choosing the outdoor unit’s spot
Every spot on a sloped lot trades something:
| Spot | What it gives you | What it costs |
|---|---|---|
| Beside the house, near the indoor unit | Short lines, simplest install | Noise near windows, decks or a bedroom |
| Downslope, away from living areas | Quiet where you sit outside | Longer lines, a built-up pad, a path for service |
| On a deck or wall bracket | No pad to build on the slope | Vibration and sound carried into the structure |
| Beside the garage | Noise kept away from living space | Longer runs if the indoor unit is at the far end |
Spec sheets list each model’s sound level in decibels, and variable-speed units spend most hours at low speed, where they are quieter. But a hard wall or a deck behind the unit can bounce sound toward the house, so the spot matters as much as the model. Placement, noise and service access are confirmed with you in writing before equipment is ordered.
Long line sets
A quiet spot is often a far one. Long refrigerant lines are routine when they stay inside the limits in the installation instructions, and the estimate should show how they are handled: run length and route, extra refrigerant for the added length, protection where the lines cross soil or follow the hillside, and insulation along the whole suction line.
New equipment often uses a different refrigerant from the system it replaces, so the old line set is reused only when its size, condition and route suit the new unit. The lines are then pressure-tested with nitrogen and pulled into a deep vacuum before refrigerant goes in. Neither step shows once the job is done, so both belong in the written scope.
The electrical panel
The panel can decide the equipment. A central AC needs its own 240-volt circuit sized to the unit’s nameplate, and a heat pump with electric backup heat may need a second, larger circuit for the indoor unit. Older panels often have no free spaces or too little spare capacity, and a long run to a distant outdoor unit may need heavier wire. We check the panel, the free breaker spaces and the existing loads in the house before recommending a model. An upgrade, a smaller backup heater or a different system goes in the estimate with its cost, not onto the install-day bill.
Heat pump, AC with a furnace, or ductless
- Heat pump. One outdoor unit cools on hot afternoons and heats on cool nights, so it works for most of the year. It can replace the furnace or pair with it. See heat pump installation.
- New AC on the existing furnace. The simplest change when the furnace is sound and the ducts can carry cooling airflow.
- New furnace with the AC. When the furnace is old, replacing both at once avoids pairing a new coil with an old blower. See furnace installation.
- Ductless. For a guest room, an addition or a space the ducts never reached: ductless mini-split installation.
From estimate to start-up
- Free estimate. Estimates for new and replacement systems are free. We walk the house and the lot, check the ducts and the panel, and look at possible spots for the outdoor unit.
- Written scope. Load assumptions; duct, electrical, thermostat, drainage and permit notes; model numbers, efficiency ratings, manufacturer warranty terms and exclusions; alternatives where they fit.
- Install day. Most replacements take 4–8 hours; a new pad, a long line run or panel work adds time. If dust, pollen or smoke days are a concern, a deeper filter cabinet is easiest to add now.
- Start-up. Charge set for the actual line length, airflow and temperature split measured, and the thermostat set up with its controls explained.
What it costs
Most AC installations in Portola Valley fall between $3,500 and $12,000. The number moves with system size and efficiency, duct repairs or airflow upgrades, electrical changes, thermostat or zoning add-ons, and equipment location and access. On hillside lots in Westridge, Blue Oaks or nearby Ladera, the pad, the line run and the path to the site are priced in the estimate up front, not added halfway through the job.