When Does the Heating Season Start in California?

The heating season in this part of California opens in November, when the average temperature first slips below the 65°F mark that utilities and climate scientists use to count heating demand. It peaks in December, runs roughly seven months, and closes out in June. Most households, though, don’t run furnaces on a fixed schedule at all here, they react to a specific cold night rather than a calendar.

When the heating season starts in California

At Los Angeles Intl AP, the reference station for this region, November is the first month whose normal mean temperature (62.3°F) drops under the 65°F baseline NOAA uses to calculate heating degree days. That’s the technical trigger: once the monthly average falls below that line, the atmosphere is officially working against your thermostat more than it’s helping it. December is the coldest month on the books, with 232 degree days, and the season doesn’t fully let go until June, when the mean climbs back above 65°F. Add it up and you get about seven months where a furnace or heat pump has at least some work to do, even if that work is light for weeks at a stretch.

That’s an average, not a forecast. A thirty-year normal smooths out the cold snaps, the December nights that dip into the 40s, the freak March storm, all of it gets folded into one tidy monthly number. The first night you’ll actually want the heat on could land in October, well before the “official” start the data points to.

The shape of the season matters more than the start date, and this table shows it month by month.

Notice how the numbers ramp up gradually through fall, hold near their peak from November through March, then fall off a cliff by May. There’s no sharp on/off switch here. It’s a long, gentle taper on both ends, which is exactly why so many households treat the thermostat as optional most of the season and only lean on it hard during the December-through-March stretch.

How hard the winter works here

Add up all twelve months and this station lands at about 1,214 heating degree days a year. Degree days function as a rough stand-in for fuel use, so a house sitting at 2,400 degree days is burning roughly twice what a house at 1,200 burns to stay comfortable, all else being equal. At 1,214, this territory sits toward the mild end of the spectrum for a place that still gets a genuine, months-long heating season.

What the annual number can’t tell you is whether that heat load arrives all at once or gets spread thin. Two places can share the same yearly total and feel completely different to live in: one might pack most of its degree days into a brutal six-week freeze, the other might spread a similar total across a long, mild, barely-there season. The monthly table above answers that question for this location, and the answer is clear. This is a long, mild season, not a short, sharp one. December and January carry real weight, but nothing here resembles a punishing cold snap month after month. That’s a meaningful distinction for anyone sizing a system or budgeting fuel, because a furnace built to survive a short brutal winter elsewhere is often oversized for the gentler, extended demand pattern typical of this region.

What most homes in California actually heat with

Federal survey data on this state’s housing stock shows a clear lean toward gas-fired central heat, with a smaller electric-heat contingent and almost nothing running on boilers or oil.

The table mixes two different breakdowns from the same federal survey, equipment type and fuel type, because that’s how the data is published. Read it as two overlapping snapshots of the same housing stock rather than one single list. “None reported” for fuel oil doesn’t mean nobody in the state uses it; it means the survey turned up too few households burning it to publish a reliable figure.

A furnace being the most common system in this state says nothing about whether it’s the right system for a particular house. It mostly reflects that natural gas was cheap and widely piped in when a lot of this housing stock went up. What a gas furnace is genuinely good at is delivering fast, forceful heat to a whole house quickly, which matters less here given how mild the season runs, but still matters on the coldest nights. Where furnaces struggle is uneven heating in rooms far from the ductwork, and dry indoor air during long cold stretches. The one maintenance item that quietly wrecks efficiency if skipped is the air filter. A clogged filter chokes airflow, forces the blower to work harder, and can shorten the life of the whole unit, and it’s the cheapest fix on the entire list below.

Run it once before you need it

The smart move is testing the system in November, before the first real cold snap sends every HVAC technician’s schedule underwater. Waiting until the coldest night of the year to discover a dead igniter or a clogged filter means a cold house and a long wait for a callback. Work through these steps in order, the first few catch most problems and cost nothing but time.

1. Turn the thermostat down, then back up several degrees above room temperature, and listen for the system to kick on within a minute or two. Let it run a short cycle and note any grinding, clicking, or rattling that wasn’t there last season.
2. Expect a faint burning-dust smell the first time the system fires after months of sitting idle. That’s dust burning off the heat exchanger or elements, and it should fade within twenty or thirty minutes. A smell that lingers or gets stronger is not normal.
3. Check the air filter and replace it if it’s visibly gray or clogged. This single step affects airflow, efficiency, and how evenly heat reaches every room in the house.
4. Walk the house and clear anything blocking a vent, a radiator, or the outdoor unit of a heat pump, furniture, curtains, stored boxes, fallen leaves, all of it restricts airflow and makes the system work harder for less heat.
5. Test the carbon monoxide alarm’s function button and confirm it’s within its stated replacement window. Combustion appliances that aren’t venting properly can produce carbon monoxide, and a working alarm is the cheap insurance against that risk.
6. If the system won’t stay running, trips a breaker, or you smell gas rather than dust, stop and call a licensed technician instead of troubleshooting further yourself.

Even a system that passes every one of these checks can still be losing heat before it ever reaches a room. According to the U.S. Department of Energy, “in a typical house, about 20%-30% of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts.” That’s not a flaw you’ll hear or smell. It shows up as a room that never quite warms up, or a system that runs longer than it should for the temperature outside.

What turning it down is actually worth

The Department of Energy puts a number on the value of backing off the thermostat rather than leaving it at one setting all day: “You can save as much as 10% a year on heating and cooling by simply turning your thermostat back 7-10°F for 8 hours a day from its normal setting.” That’s a yearly figure covering both heating and cooling combined, tied to a specific setback range held for a specific stretch of hours. It isn’t a per-degree formula, and it isn’t a winter-only number.

In a region where the heating season stretches across roughly seven months, even a mild one, that 8-hour setback window has a lot of days to work with. A programmable or smart thermostat set back overnight or during work hours captures that saving automatically, without anyone needing to remember to adjust a dial. The longer the season lingers, even at low intensity through October and May, the more those quiet hours add up.