Independent guide. Cost figures use 2026 EIA state-average residential rates. SEER2 references DOE federal efficiency standards.Verified May 2026

Cost to run an air conditioner per hour 2026: BTU and SEER2 tables

For a typical 3-ton (36,000 BTU) central AC at the minimum SEER2 14.3 standard, running cost is about 45 cents per hour at US average rates. Higher SEER2 ratings, smaller units, and TOU off-peak hours all reduce the cost meaningfully. This page provides cost-per-hour tables across the main residential AC sizes and key state rate environments, plus the runtime patterns that drive your actual monthly bill.

Cost per hour by AC size and state

Size	BTU/hr	SEER2	kWh/hr	US avg	FL (15.5c)	CA (27.3c)
1 ton	12,000	14.3	0.84	$0.15	$0.13	$0.23
1.5 ton	18,000	14.3	1.26	$0.23	$0.20	$0.34
2 ton	24,000	14.3	1.68	$0.30	$0.26	$0.46
2.5 ton	30,000	14.3	2.10	$0.38	$0.33	$0.57
3 ton	36,000	14.3	2.52	$0.45	$0.39	$0.69
3 ton (SEER2 18)	36,000	18	2.00	$0.36	$0.31	$0.55
3.5 ton	42,000	14.3	2.94	$0.53	$0.46	$0.80
4 ton	48,000	14.3	3.36	$0.61	$0.52	$0.92
5 ton	60,000	14.3	4.20	$0.76	$0.65	$1.15

Cost = kWh per hour times state retail rate. Real-world cost varies with duct loss, short-cycling, defrost cycles and ambient humidity. Inverter (variable-speed) units modulate down at partial load and use less than nameplate during steady-state operation.

Tonnage and BTU primer

AC sizing uses two conventions. Residential central AC is sized by tonnage (1 ton = 12,000 BTU/hour of cooling capacity); window units and small splits are sized by BTU directly. A typical 1,500-square-foot home in a moderate climate needs about 2 to 2.5 tons of cooling; a 2,500-square-foot home needs 3 to 4 tons; a 4,000-square-foot home needs 5 tons or two zones. Oversized units run in short cycles (turn on, cool briefly, turn off) which actually reduces dehumidification and increases per-hour run cost.

For a single room, BTU sizing is easier. A 10,000 BTU window unit handles roughly 450 square feet; 12,000 BTU handles 550; 18,000 BTU handles 1,000. ENERGY STAR maintains a sizing chart that adjusts for ceiling height, sun exposure, and occupancy that produces more accurate sizing than the simple square footage rules. Undersized units run continuously and never quite cool the space; oversized units cycle too fast. Right-sizing matters for both comfort and operating cost.

Why SEER2 matters so much

SEER2 measures the cooling output a unit produces per unit of electrical input across a full season at realistic operating conditions. The 2023 federal minimum is 14.3 SEER2 in the northern US and 13.4 in the southern US. Modern high-efficiency units rate 16 to 22 SEER2; the best variable-speed inverter units rate up to 28. A 50 percent improvement in SEER2 produces roughly 50 percent lower running cost for the same cooling load.

For a home where AC is running 1,500 hours per cooling season (a typical Sun Belt home), upgrading from SEER2 14 to SEER2 18 saves about 25 percent of the cooling kWh. At $0.45 per hour for the lower-SEER unit vs $0.36 for the higher-SEER unit, the annual savings are 1,500 hours times $0.09 = $135. Over a 15-year equipment life, the cumulative savings on rate-stable electricity is about $2,000; with rate inflation of 3 percent per year, the saving over the life is closer to $2,500. The upfront cost premium for a 2-tier SEER2 jump runs about $800 to $1,500, so the payback is typically 6 to 11 years.

Duct loss and the hidden cost of central AC

Central AC systems lose cooling capacity in the duct network between the air handler and the registers. A typical home's duct system, particularly when ducts run through an unconditioned attic, leaks 20 to 35 percent of the cooled air to outside the conditioned space, into the attic or crawl space. That leakage means the AC has to run 20 to 35 percent longer to deliver the same cooling at the register, which is 20 to 35 percent more kWh and 20 to 35 percent more cost.

Duct sealing (with mastic at every joint, not just tape) typically reduces leakage to 5 to 10 percent and costs $500 to $1,500 for a professional service. The payback in a hot climate with heavy AC use is 2 to 4 years, sometimes less. ENERGY STAR and many utility efficiency programs subsidise duct sealing, often making it a net-zero-cost improvement for the homeowner. Aeroseal is a commercial duct-sealing service that uses aerosolised sealant blown through the duct system; it is more expensive ($1,500 to $3,000) but produces near-zero leakage and is the right call for homes with severe duct issues.

Short-cycling: when an oversized AC costs you money

Oversized AC units cool the home quickly and shut off, then turn back on a short time later when the temperature rises. This cycling looks efficient (the unit is off most of the time) but it has two cost-related downsides. First, AC compressors draw 3 to 5 times their nameplate current during startup; short-cycling means many startups per hour, each consuming more energy than steady-state operation. Second, short cycles do not run long enough to dehumidify; the AC removes the sensible heat (temperature) without removing the latent heat (moisture), leaving the home cooler but more humid.

The fix for short-cycling is right-sizing on AC replacement (use a Manual J load calculation, not the lazy "match the existing unit size" approach) and, where possible, choosing a variable-speed inverter compressor that can modulate down to 30 to 50 percent of nameplate at partial load. Variable-speed units run more continuously at lower capacity, which improves dehumidification and reduces start-up surge cost. The trade-off is higher upfront cost (typically $1,500 to $3,000 premium over single-stage equivalent), justified mostly by comfort improvement and partly by efficiency gain.

Thermostat strategies that move the needle

Five thermostat strategies that reduce cooling cost without sacrificing comfort. First, set back to 80 to 82 when the home is unoccupied during the day; let the smart thermostat learn the cooling-recovery time and start pre-cooling 30 to 60 minutes before scheduled occupancy. Second, raise the night setpoint by 2 to 4 degrees; the body cools more easily at night and a 78-degree bedroom is comfortable for most sleepers. Third, use ceiling fans to circulate air; a fan on at 4 mph creates a perceived 4 degree cooling effect at no AC cost. Fourth, close blinds on south- and west-facing windows during the late afternoon to reduce solar gain. Fifth, on TOU plans, pre-cool to 72 at 3pm and let the home drift to 78 between 4pm and 9pm peak; the smart thermostat can manage this automatically.

Smart thermostat models that handle this well include Ecobee Premium (with multiple temperature sensors for whole-house averaging), Google Nest Learning Thermostat (with auto-learning and presence detection), and Honeywell T9 (with room sensors and geofencing). The thermostat itself costs $150 to $250; the smart-control savings typically pay for the thermostat within the first cooling season for any household with meaningful AC use. Many utilities (including PG&E, ConEd, Xcel, Duke) offer instant rebates of $50 to $100 on qualifying smart thermostats, reducing the net cost further.

Sources and further reading

FAQ

How much does it cost to run an AC for one hour?

At the US national average electricity rate of 18.05 cents per kWh, a 3-ton (36,000 BTU) central AC running at a SEER2 rating of 14 draws about 2.6 kWh per hour and costs about 47 cents per hour. The same unit at SEER2 18 (a modern high-efficiency variant) draws about 2.0 kWh per hour and costs 36 cents. A typical 8-hour AC day costs $3 to $4 in moderate climates and $5 to $8 in hot climates with longer run times.

What does the SEER2 rating mean?

SEER2 (Seasonal Energy Efficiency Ratio, second edition) measures how much cooling output a unit produces per unit of electrical input across a full cooling season, including realistic operating conditions. Federal minimum SEER2 for new central AC units is 14.3 in the northern US and 13.4 in the southern US (since 2023). Modern high-efficiency units rate 16 to 22 SEER2; variable-speed inverter units rate up to 28. A 50 percent improvement in SEER2 produces roughly 50 percent lower running cost for the same cooling.

How much does a window AC cost per hour?

A 10,000 BTU window AC at EER 12 (typical mid-range) draws about 0.83 kWh per hour and costs about 15 cents per hour at the national average rate. A 12,000 BTU window unit costs about 18 cents per hour. Window units run less efficiently than central systems per BTU, but the actual hourly cost is lower because they cool a smaller area; if you only need to cool a bedroom or single room, a window unit is much cheaper to run than central AC chilling the whole house.

Does running the AC longer at a higher setpoint save money?

Generally yes. Raising the thermostat setpoint by 1 degree saves about 3 to 5 percent on cooling cost. Going from 72 to 78 saves 18 to 30 percent. The savings compound across a long cooling season. The exception: humid climates where dehumidification matters (Florida, Gulf Coast). At very high setpoints (above 80) the AC may not run long enough to remove humidity, leaving the home muggy. In those climates, pair a moderate setpoint (76 to 78) with a dehumidifier or with a variable-speed AC that can run continuously at low capacity.

How much does central vs ductless mini-split cost?

Ductless mini-splits typically run 20 to 40 percent cheaper than central AC for the same cooling load because they eliminate duct losses (which can be 20 to 35 percent in poorly insulated attics) and they only cool the zones you are using. A 3-ton single-zone mini-split at SEER2 22 running 8 hours per day costs about $1.80 to $2.40 per day at national average rates versus $3 to $4 for an equivalent central system. The trade-off is upfront cost ($4,000 to $8,000 per zone installed) and the cosmetic impact of the indoor wall heads.

Does running AC at night cost less on TOU?

Yes, substantially. On most TOU plans (PG&E EV2-A, ConEd Smart Home Rate, Duke TOU-E, etc.), off-peak rates are 30 to 70 percent below peak rates. A 2.5 kWh-per-hour AC running 6 hours overnight on PG&E EV2-A off-peak costs about $4.65 vs $9.30 on peak. Pre-cooling the home before peak hours and letting temperature drift up during peak can cut summer cooling cost by 25 to 40 percent on TOU plans with no comfort loss when paired with a smart thermostat.

How much does it cost to run AC 24 hours a day?

A 3-ton central AC at SEER2 14 running continuously for 24 hours uses about 62 kWh and costs $11.20 at the national average. In hot states (Florida, Texas, Arizona) where this happens during August heat waves, the monthly AC cost can exceed $350 for a typical home. Reducing the runtime by improving home insulation, adding attic ventilation, raising the setpoint by 2 to 4 degrees, and replacing an old unit with a higher SEER2 model can cut that to under $200 per month.

Disclaimer. Cost-per-hour figures use 2026 EIA state-average residential rates, nameplate kWh consumption based on stated SEER2 ratings, and assume steady-state operation. Real-world cost varies by climate, home insulation, duct condition, humidity and operating patterns. Use the tables as benchmarks, not exact billing predictions.