Running a central AC in San Diego costs roughly $1.20 to $1.75 for every hour the compressor runs. A typical residential unit draws about 3 to 3.5 kilowatts while it’s actually cooling, and SDG&E charges somewhere between $0.40 and $0.50 per kilowatt-hour depending on your plan and the time of day, well above the national average of around $0.16/kWh. Multiply the draw by your rate and you get the real number for your house. Everything below shows you how.
Most articles on this topic use national averages that don’t apply here. San Diego pays some of the steepest residential electricity rates in the country, so a formula built on $0.16/kWh gives you a number that’s less than half of what your SDG&E bill will actually show. The formula matters more than any single answer, because your rate, your tonnage, and your runtime are all different from the next house over.
How much electricity does a central AC use?
A central AC’s power draw depends almost entirely on its size, measured in tons of cooling capacity. The compressor is what pulls the power. The blower fan draws very little by comparison, usually under 500 watts. Here’s the typical range by system size.
| AC size (tons) | Typical draw (running) | Approx. cost per hour at $0.45/kWh |
|---|---|---|
| 2 ton | 2.0-2.5 kW | $0.90-$1.13 |
| 3 ton | 3.0-3.5 kW | $1.35-$1.58 |
| 4 ton | 4.0-4.5 kW | $1.80-$2.03 |
| 5 ton | 4.5-5.0 kW | $2.03-$2.25 |
Most San Diego single-family homes run a 3 to 4 ton system, so $1.35 to $2.00 an hour of actual runtime is the range that applies to most of us. Higher SEER2 systems pull less power for the same cooling output, which we get into further down.
How do you calculate what it costs to run per hour?
The formula is simple: kilowatts drawn times your electricity rate equals cost per hour of runtime. Written out, it’s kW x $/kWh = cost per hour. Plug in a 3.5 kW unit and a $0.45/kWh rate and you get 3.5 x 0.45 = $1.58 an hour. That’s the cost to run central AC while the compressor is actually cycling, not the cost for the whole hour if your AC is only running part of it.
This is the piece most calculators skip. Your AC doesn’t run continuously even on a 100-degree day. It cycles on and off as the thermostat calls for cooling. So the real question isn’t just the hourly rate, it’s how many hours the compressor actually runs in a day.
What does it cost to run per day and per month in San Diego?
Daily and monthly cost is the hourly figure multiplied by how many hours the compressor actually runs, and that number varies enormously across San Diego County. The formula stays the same: kW x hours of runtime x $/kWh x number of days. Only the hours change.
Coastal homes in places like La Jolla, Del Mar, or Ocean Beach often see marine layer and onshore breeze keep indoor temperatures manageable. A coastal 3-ton system might run 2 to 4 hours a day even during a warm stretch. At $1.58/hr, that’s roughly $3 to $6 a day, or $95 to $190 across a 31-day month.
Inland homes tell a different story. Escondido, El Cajon, Santee, and the rest of East County routinely hit 90-plus degrees for stretches of summer, and a 3 to 4 ton system there can run 6 to 10 hours a day or more. At $1.58 to $2.00/hr, that’s $10 to $20 a day, or $300 to $620 across a month of sustained heat. That’s the gap between a manageable SDG&E bill and one that makes you want to call someone.
These are ranges built from the formula, not a single promised number. Your actual bill depends on your system’s tonnage, your home’s insulation and orientation, your thermostat setting, and how many days actually hit peak heat that month.
Why does running AC cost more in San Diego than almost anywhere else?
Running AC costs more here mainly because SDG&E’s rates are among the highest in the nation, not because San Diego air conditioners use more power than anywhere else. The equipment math is the same everywhere. The rate you’re charged per kilowatt-hour is what changes the answer, and SDG&E sits at roughly two to three times the national average.
On top of that, most SDG&E residential customers are on a time-of-use plan, which means the price per kilowatt-hour is not flat across the day. The 4pm to 9pm window on weekdays is priced highest, often significantly above the midday rate. That window also happens to overlap with when San Diego homes are hottest and AC demand peaks, which is the worst possible combination for your bill. Running the same AC at noon instead of 6pm can cost meaningfully less per hour, even though the equipment and the outdoor temperature haven’t changed.
Pre-cooling your house in the early afternoon, before the peak window starts, and letting it coast through the expensive hours is one of the simplest ways to shift cost out of the priciest part of the day. We cover why your SDG&E bill is so high in more depth if you want the full picture beyond just AC.
How much can you cut the running cost?
The two levers that actually move this number are how efficient your equipment is and how many hours it runs, and both are things you can act on without changing the physics above. A higher SEER2 rating means fewer kilowatt-hours for the same amount of cooling, so the kW side of the formula drops. Shifting more of your runtime outside the 4pm to 9pm peak window lowers your effective $/kWh. We’ve written a full breakdown of how to cut your AC bill this summer with the specific tactics, so we won’t repeat that here. If your system is old, checking whether a SEER2 rating upgrade pencils out is worth the ten minutes it takes to read. And if you’re already generating your own power, solar and NEM 3.0 changes the math on when running AC is effectively free versus when it’s still drawing from the grid at full price.
Regular maintenance keeps efficiency up too. A dirty coil or a low refrigerant charge makes a 3-ton system pull more like a 4-ton system’s worth of power for the same cooling, which quietly inflates every number in this article. Routine HVAC maintenance on a normal schedule prevents that drift before it shows up on a bill.
Frequently asked questions
How much does it cost to run AC for 24 hours in San Diego?
Running AC for 24 straight hours would cost roughly $35 to $50 for a typical 3.5 kW system at San Diego rates, but almost no home actually needs the compressor running the full 24 hours. Real-world cycling means actual compressor runtime is usually 4 to 12 hours a day depending on location and heat, which is why the daily estimates above land closer to $3 to $20 rather than the full 24-hour math.
Does a newer, higher-SEER2 AC cost less to run?
Yes, a higher SEER2 rating directly lowers the kilowatts drawn for the same amount of cooling output. A modern 18 to 20 SEER2 system can use 30 to 40 percent less electricity than an older 10 to 13 SEER unit doing the same job, which shows up as a real drop in the kW side of the cost formula.
Is it cheaper to leave the AC on all day or turn it off?
Cycling with a programmable schedule is generally cheaper than running continuously at a low temperature all day. Letting the house drift a few degrees warmer while you’re out, then cooling back down before you’re home, uses less total energy than holding one temperature around the clock, especially if the cool-down happens before the 4pm to 9pm peak window.
How many watts does a 3-ton AC use?
A typical 3-ton (36,000 BTU) central AC draws about 3,000 to 3,500 watts, or 3 to 3.5 kW, while the compressor is actively cooling. That figure is for the compressor and condenser fan together. The indoor blower adds a few hundred more watts on top of that.
Why is my AC the biggest part of my SDG&E bill?
Your AC is the single largest electrical load in most San Diego homes during summer because nothing else in the house draws 3,000-plus watts for hours at a stretch. A refrigerator, a TV, and lighting combined don’t come close to matching what a compressor pulls, and San Diego’s high per-kWh rate multiplies that gap into a large share of the total bill.
When is the most expensive time to run my AC in San Diego?
The 4pm to 9pm window on weekdays is the most expensive time under SDG&E’s standard time-of-use plans. That window also overlaps with peak outdoor heat in most of the county, which means the hours you’re most tempted to crank the AC are the same hours it costs the most to do it.
Get a straight answer for your home
Every house is different, and the ranges above only get you so far without knowing your system’s tonnage, your rate plan, and how your home actually holds heat. If you want help figuring out what your AC is actually costing you, or whether an AC tune-up or a repair would bring that number down, we can connect you with HVAC pros in the San Diego network who cover the whole county, coastal to inland, including Escondido and the rest of North County inland where runtime hours run highest. Call (442) 777-6440, or start with AC repair if your system is already struggling to keep up.