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Sizing a heat pump for this county means working out what the system has to deliver on its coldest nights, not its average ones. Homes in San Mateo County, CA run heat about seven months a year, from November through May. A heat pump loses capacity as outdoor temperatures drop, so a contractor has to establish the lowest temperatures the equipment will face before settling on a model and a backup heat strategy. Undersizing shows up fast here because the heating season is long enough that a system with too little cold-weather capacity leans on its resistance backup strip repeatedly, which is the most wear-intensive way a heat pump can operate. The load calculation is the install.
Ductwork laid down for a furnace and central air setup rarely moves air the way a heat pump needs it to. Half the homes in San Mateo County, California were built in 1966 or earlier (2020-2024 ACS 5-year). That gap between what the house was built around and what a new heat pump demands is where installation jobs here get complicated: a contractor checking existing duct diameter, condition, and routing before committing to a layout is doing the work the age of the stock makes necessary. Electrical service gets the same scrutiny, because a panel sized for the original load may not carry what a new heat pump draws.
What a Heat Pump Installation Puts in Your Home
The outdoor unit is the piece most homeowners see first, mounted on a concrete pad or wall bracket beside the house, housing the compressor and the coil that exchange heat with the outside air. Inside, an air handler sits in a utility closet, basement, or attic and moves conditioned air through the home. Together these two cabinets are the core of what gets installed.
A refrigerant line set runs between the outdoor and indoor units, typically along an exterior wall, carrying the refrigerant that links the two sides of the system. A thermostat goes on an interior wall and gives the homeowner control over the whole setup. Some installations also include a supplemental electric heat strip inside the air handler for the coldest days.
The drawing shows a typical layout, and a licensed contractor determines exactly what configuration applies to your house.
Get matched in San Mateo CountySan Mateo County, by the record
282 severe weather events were recorded in San Mateo County, California between 2015 and 2024.
NOAA National Centers for Environmental Information, Storm Events Database, bulk CSV export, events 2015-01-01 through 2024-12-31.Half the homes in San Mateo County, California were built in 1966 or earlier (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesSan Mateo County, California holds 287,184 housing units (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesOwners occupy 58.5% of the occupied homes in San Mateo County, California (2020-2024 ACS 5-year).
U.S. Census Bureau, 2020-2024 American Community Survey 5-Year EstimatesHeat Pump Installation Rules for San Mateo County, California1 codes, standards, and laws
Licensing Rules for San Mateo County, California
California requires a state contractor license: it is a misdemeanour to engage in the business of, or act in the capacity of, a contractor in California without one, unless the work is exempt.
Weather Events in San Mateo County
Heat pump performance is sized against the climate it works in, and climate here is not abstract. Storms, temperature swings, and humidity all shape how hard the equipment runs and what a properly specified installation looks like for this area.
282 severe weather events, 2015–2024. Source: NOAA National Centers for Environmental Information, Storm Events Database.