Running AC in San Diego costs roughly $22 to $440 a month. Coastal homes with an efficient system land near the low end, often under $50. Inland homes running an old central AC through a heat wave hit the high end. The driver is two things: how efficient your system is, and how many hours it actually runs. The table below shows the math by system type, using current SDG&E rates.
Your neighbor in Carlsbad pays almost nothing to cool. Your cousin in El Cajon dreads the SDG&E bill all summer. Same county, very different numbers. Here’s why, with the math shown so you can plug in your own usage.
The rate that drives everything: SDG&E per kWh
SDG&E has some of the highest residential electricity rates in the country. As of January 2026, the bundled residential average sits around 45.7 cents per kWh for customers who buy both delivery and generation from SDG&E (SDG&E total electric rates). Time-of-use plans push peak rates above 60 cents and drop off-peak to the mid-30s.
For the math in this post, we use a round 46 cents per kWh. Your real rate depends on your plan, your baseline tier, and whether you get generation through a community choice program. Pull the actual number off your bill and swap it in.
The formula is simple: watts × hours × days ÷ 1,000 × your rate. That gives you monthly cost. Everything below is that one formula, run for different systems and usage levels.
Monthly cost to run AC by system type
This table covers the five most common ways San Diego homes get cooled. Coastal usage assumes light running, the way most beach-area homes use AC. Inland usage assumes heavy running through the warm season. Costs use 46 cents per kWh.
| System type | Typical draw | Coastal (light use) | Inland (heavy use) |
|---|---|---|---|
| Old central AC (10–13 SEER) | ~4,000 W | ~$74/mo | ~$440/mo |
| New high-SEER central AC (16–20 SEER) | ~2,000 W | ~$37/mo | ~$221/mo |
| Heat pump (cooling mode) | ~2,000 W | ~$37/mo | ~$221/mo |
| Window unit (single room) | ~1,100 W | ~$40/mo | ~$121/mo |
| Mini split (single zone) | ~1,200 W | ~$22/mo | ~$133/mo |
The single biggest takeaway: an old central AC inland can cost more than five times what a mini split costs coastal. Efficiency and runtime do the heavy lifting, not the brand on the box.
Show me the math
No magic here. Each number above is the same formula run with real inputs. Central AC draw figures come from the U.S. Department of Energy and standard wattage references; central units pull 3,000 to 5,000 watts.
Old central AC, coastal. Light use means roughly 2 hours a day, 20 days a month. That’s 40 hours. 4,000 W × 40 hrs ÷ 1,000 = 160 kWh. 160 × $0.46 = $73.60.
Old central AC, inland. Heavy use means roughly 8 hours a day, every day. That’s 240 hours. 4,000 W × 240 hrs ÷ 1,000 = 960 kWh. 960 × $0.46 = $441.60.
New high-SEER central AC, inland. Same 240 hours, half the draw. 2,000 W × 240 hrs ÷ 1,000 = 480 kWh. 480 × $0.46 = $220.80.
Mini split, coastal. Single-zone units pull around 1,200 watts. At 40 hours: 1,200 W × 40 hrs ÷ 1,000 = 48 kWh. 48 × $0.46 = $22.08.
That’s the whole method. Change the hours to match your habits, change the rate to match your bill, and you have your own number.
Coastal vs inland: the real cost gap
The biggest variable in San Diego isn’t your equipment. It’s your zip code. Coastal San Diego stays mild because of cool onshore flow off the Pacific. The median warm-season temperature near the coast runs about 76 degrees, versus 83 degrees inland (NIH study on San Diego climate zones).
That difference shows up on your bill. A home in Encinitas or Carlsbad might run AC a few hours on a handful of warm afternoons. A home in El Cajon or Escondido runs it most of the day from June through September. Same system, three to five times the monthly cost.
If you live coastal, your monthly AC cost is small no matter what you own. If you live inland, your equipment choice matters enormously. The difference between an old 12-SEER unit and a new 18-SEER one can be over $200 a month at peak. Want the full set of tactics to bring that down, see our guide on lowering your AC bill in San Diego summer.
Why efficiency cuts the number in half
SEER measures how much cooling you get per watt. A higher number means less electricity for the same comfort. An old 10-SEER system and a new 18-SEER system can cool the same house, but the new one does it on roughly half the power.
At SDG&E rates, that gap is money. Cut 480 kWh a month down to 240 and you save about $110 every billing cycle in peak season. Over a summer, that adds up to real savings, which is why a new AC installation or a heat pump often pays back faster in San Diego than in cheaper-power states.
Maintenance matters too. A dirty filter, low refrigerant, or a clogged coil makes any system pull more watts for less cooling. A yearly AC maintenance tune-up keeps the draw where it should be, and a clean system can cut runtime noticeably.
If you’re wondering whether it’s even safe or smart to leave it running all day, that’s a different question with its own answer, see can I run my AC 24/7 in San Diego.
How to lower your monthly AC cost
A few levers move the number the most. Raise your thermostat a few degrees, since each degree cooler costs more watts. Run AC during off-peak hours if you’re on a time-of-use plan. Use ceiling fans to feel cooler at a higher setpoint. Seal leaks and shade west-facing windows so the system runs fewer hours.
The biggest lever is the equipment itself. If you’re running a 12-plus-year-old central system inland, the monthly cost alone can justify an upgrade. An efficient system or a clean tune-up cuts the number directly. We can run the math on your actual home and tell you what an upgrade would save, no pressure either way. Call us at (442) 777-6440 for an assessment.
FAQs
How much does it cost to run AC in San Diego per month?
Most San Diego homes spend $22 to $440 a month on AC. Coastal homes with an efficient system often pay under $50, because they run the AC only a few hours on warm afternoons. Inland homes running an older central system through a heat wave reach the high end. Your number depends on system efficiency, hours of runtime, and your SDG&E rate, which averages about 46 cents per kWh in 2026.
Is it cheaper to run AC or a fan in San Diego?
A fan is far cheaper. A ceiling fan pulls 15 to 90 watts, while a central AC pulls 2,000 to 4,000. Running a fan all day costs pennies. But a fan only moves air, it doesn’t lower the temperature. The smart move in San Diego is both: set the AC a few degrees higher and use fans to feel cooler. That cuts AC runtime and your bill at the same time.
How much does a new efficient AC save per month?
Swapping an old 10-to-13-SEER central unit for a new 16-to-20-SEER one roughly halves the power draw. For an inland home running heavy in summer, that’s a drop from around $440 to about $221 a month, a savings near $200 at peak. Coastal homes save less in dollars because they run fewer hours, but the percentage savings is the same.
Does a heat pump cost more to run than AC?
No. In cooling mode, a heat pump uses about the same electricity as a comparable high-efficiency AC, roughly $37 a month coastal and $221 inland for heavy use. The advantage is heating: a heat pump also heats your home efficiently, often cheaper than a gas furnace or electric resistance heat, so it can lower your year-round energy cost. See our heat pump service page for details.
Why is my SDG&E bill so high when I barely run the AC?
SDG&E rates are among the highest in the nation, around 46 cents per kWh in 2026, and they jump during peak hours on time-of-use plans. Even modest AC use shows up fast at those rates. An old or poorly maintained system makes it worse, since it pulls more watts for the same cooling. Check your rate plan, run AC off-peak when possible, and get a tune-up if the system is older.
How do I calculate my own AC cost?
Use this formula: watts × hours per day × days ÷ 1,000 × your rate. Find your system’s wattage on the unit label or by dividing its BTU rating by its SEER. Estimate how many hours a day it actually runs. Pull your rate per kWh off your SDG&E bill. Plug the numbers in and you’ll have your real monthly cost.