Central air installation means putting in a complete ducted system: an air handler or furnace, a cooling coil, an outdoor unit, supply and return ducts, registers, a thermostat, and the power and drain to run it all. It is the job for a house that has never had ducts, or whose old ducts are too small, too leaky or in the wrong places to reuse. In Menlo Park, Atherton and Portola Valley that is often an older home heated by a wall furnace, a floor furnace or hot-water radiators, or a house where additions left the original duct system behind. If you already have a working furnace and sound ducts, adding cooling is a smaller job: see AC installation.
How to get central air, step by step
- Survey. Attic height and access, crawlspace depth, closets and soffits that could carry a duct, the electrical panel, and candidate spots for the air handler and the outdoor unit.
- Room-by-room load calculation (the Manual J method). Each room’s heat gain through windows, walls and roof sets how much air it needs. This step prevents the hot back bedroom and the over-cooled living room.
- Duct design (the Manual D method). Trunk and branch sizes, register locations and return paths, drawn on a plan.
- Equipment choice. A gas furnace with an AC coil, or a heat pump with an electric air handler that heats and cools.
- Written estimate. Free for new systems, showing the layout, the equipment and every line of work.
- Install and balance. Ducts and equipment go in, the system is started, and airflow is measured and set room by room.
Does your house have room for ducts?
| House | Usual approach |
|---|---|
| Single-story ranch with an attic | Air handler in the attic or garage; ducts across the attic, registers in the ceilings |
| Single-story over a crawlspace | Floor registers fed from below; air handler in a closet or the crawlspace |
| Two stories | Two systems, or one system feeding upstairs from the attic and downstairs from below |
| Vaulted ceilings, no attic | Ducts in built soffits or chases, or ductless units for those rooms |
| Large house with separate wings | Two or more systems, or one system with zone dampers |
Large Atherton homes often end up with two systems or zones, because one long trunk cannot carry enough air to the far end of a big house. Equipment can sit in an attic, a basement or a side-yard enclosure, and each choice changes the noise, the service access and the duct lengths.
Getting the ducts right
Most of the comfort in central air comes from the ducts, not the outdoor unit.
- Returns where people close doors. A bedroom with the door shut needs its own return or a transfer grille; without one, the room pressurizes and gets little supply air.
- Insulated, sealed runs. Attic ducts over a ranch home sit in very hot air on summer afternoons. Sealed joints and proper duct insulation matter as much as the efficiency label on the outdoor unit, and older ranch homes with patchy attic insulation may want insulation work priced alongside.
- Sizes that keep air quiet. Correct duct and register sizes keep air velocity low, so the system is quiet.
- A filter you will actually change. A filter cabinet sized for a deeper, finer filter improves filtration without choking airflow, which helps on dusty, pollen-heavy or smoky days.
If you are unsure whether insulation and air sealing should come before the new system, an energy audit answers that before sizing.
What the price covers
A typical full central air system costs $5,000 to $15,000 and takes one to two days. Where a job lands depends on:
- feet of duct, and the number of registers and returns;
- how easy the attic and crawlspace are to work in;
- furnace plus AC, or heat pump plus air handler;
- capacity and efficiency;
- electrical work, including a new circuit or panel space;
- chases or soffits needed to hide ducts in finished rooms, and who patches the drywall.
A house that needs two systems is a larger scope than one, and the free written estimate prices exactly what your house needs, with model numbers, the duct plan, warranty terms and exclusions spelled out.
The install days
Day one is mostly ductwork: trunks and branches in the attic or crawlspace, register and return openings cut, the air handler or furnace set. Day two brings the outdoor unit, line set, electrical and drain connections, the thermostat, start-up, the refrigerant charge set by measurement, and airflow balancing. Smaller houses can finish in a day; large or two-system homes take longer.
Local notes
On Portola Valley hillside lots the only level spot for the outdoor unit may be well away from the house, which means longer refrigerant and electrical runs and some planning for the slope. Under the mature shade trees common in Menlo Park, an outdoor unit set beneath branches collects leaves; open sky above it saves coil cleaning later. Summers here are warm and dry with hotter spells, so the first hot week is the real test: that is the time to check room temperatures and fine-tune dampers. A smart thermostat and zoning can be planned in from the start.