A single-zone 12,000 BTU mini split costs $25–$75 per month to run for cooling and $30–$100 per month for heating, depending on your electricity rate, climate, and unit efficiency. At the national average of $0.17/kWh, a 12K unit with SEER2 20 costs approximately $35/month for cooling when running 8 hours daily — about $1.17 per day.
Your actual cost depends on four variables: the unit's BTU size, its efficiency rating (SEER2 for cooling, HSPF2 for heating), daily run hours, and your local electricity price. Use the calculator below to get your specific number, or scroll down for comprehensive cost tables covering every common scenario.
Monthly Running Cost by Mini Split Size
Cooling Season Costs (8 Hours/Day Average)
These tables use the national average electricity rate of $0.17/kWh. Adjust proportionally for your local rate.
| Unit Size | SEER2 15 | SEER2 18 | SEER2 20 | SEER2 22 | SEER2 25 | SEER2 30 |
|---|---|---|---|---|---|---|
| 9,000 BTU | $24/mo | $20/mo | $18/mo | $17/mo | $15/mo | $12/mo |
| 12,000 BTU | $33/mo | $27/mo | $24/mo | $22/mo | $20/mo | $16/mo |
| 15,000 BTU | $41/mo | $34/mo | $31/mo | $28/mo | $24/mo | $20/mo |
| 18,000 BTU | $49/mo | $41/mo | $37/mo | $33/mo | $29/mo | $24/mo |
| 24,000 BTU | $65/mo | $54/mo | $49/mo | $44/mo | $39/mo | $33/mo |
| 30,000 BTU | $82/mo | $68/mo | $61/mo | $56/mo | $49/mo | $41/mo |
| 36,000 BTU | $98/mo | $82/mo | $73/mo | $67/mo | $59/mo | $49/mo |
Heating Season Costs (10 Hours/Day Average)
Heating costs use HSPF2. Higher HSPF2 = lower operating cost. Heating season daily run hours are typically longer than cooling.
| Unit Size | HSPF2 8.0 | HSPF2 9.0 | HSPF2 10.0 | HSPF2 11.0 | HSPF2 12.0 | HSPF2 13.0 |
|---|---|---|---|---|---|---|
| 9,000 BTU | $29/mo | $26/mo | $23/mo | $21/mo | $19/mo | $18/mo |
| 12,000 BTU | $38/mo | $34/mo | $31/mo | $28/mo | $26/mo | $24/mo |
| 15,000 BTU | $48/mo | $43/mo | $38/mo | $35/mo | $32/mo | $29/mo |
| 18,000 BTU | $58/mo | $51/mo | $46/mo | $42/mo | $38/mo | $35/mo |
| 24,000 BTU | $77/mo | $68/mo | $61/mo | $56/mo | $51/mo | $47/mo |
| 30,000 BTU | $96/mo | $85/mo | $77/mo | $70/mo | $64/mo | $59/mo |
| 36,000 BTU | $115/mo | $102/mo | $92/mo | $84/mo | $77/mo | $71/mo |
Reading these tables: Find your unit size in the left column, then find the closest SEER2 or HSPF2 rating across the top. The cell gives your estimated monthly cost at $0.17/kWh. If your electricity rate is different, multiply the table value by (your rate ÷ 0.17). For example, if you pay $0.25/kWh, multiply each value by 1.47.
The Running Cost Formula
Here's the exact math behind every number in this guide:
Monthly Cooling Cost = (BTU ÷ SEER2 × Hours/Day × 30) ÷ 1,000 × $/kWh
Monthly Heating Cost = (BTU ÷ HSPF2 × Hours/Day × 30) ÷ 1,000 × $/kWh
Where BTU is your unit's capacity, SEER2/HSPF2 is the efficiency rating, Hours/Day is your average daily run time, and $/kWh is your electricity rate.
Worked Example 1: Single Bedroom Mini Split in Phoenix
Setup: 9,000 BTU MrCool DIY 4th Gen (SEER2 22), Phoenix, AZ electricity at $0.13/kWh, running 12 hours/day during summer.
- Monthly cooling cost = (9,000 ÷ 22 × 12 × 30) ÷ 1,000 × $0.13
- = (409 × 12 × 30) ÷ 1,000 × $0.13
- = 147,272 ÷ 1,000 × $0.13
- = 147.3 kWh × $0.13
- = $19.15/month
- Phoenix cooling season: 7 months (April–October)
- Annual cooling cost: $134
Worked Example 2: Living Room Mini Split in New York
Setup: 18,000 BTU Mitsubishi (SEER2 26, HSPF2 12), New York electricity at $0.24/kWh, cooling 8 hours/day summer, heating 14 hours/day winter.
Cooling (June–September):
- Monthly = (18,000 ÷ 26 × 8 × 30) ÷ 1,000 × $0.24
- = 166.2 kWh × $0.24
- = $39.88/month cooling
- 4 months × $39.88 = $159.52 annual cooling
Heating (November–March):
- Monthly = (18,000 ÷ 12 × 14 × 30) ÷ 1,000 × $0.24
- = 630 kWh × $0.24
- = $151.20/month heating
- 5 months × $151.20 = $756 annual heating
- Total annual HVAC cost: ~$916
Worked Example 3: Whole-Home Multi-Zone in Atlanta
Setup: Daikin 5-zone system: 48,000 BTU outdoor unit with five 9,600 BTU indoor zones (SEER2 19, HSPF2 10.5). Atlanta electricity at $0.14/kWh. Average 3 zones active, cooling 10 hrs/day summer, heating 12 hrs/day winter.
Cooling (May–September):
- Active capacity: 3 × 9,600 = 28,800 BTU
- Monthly = (28,800 ÷ 19 × 10 × 30) ÷ 1,000 × $0.14
- = 454.7 kWh × $0.14
- = $63.66/month cooling
- 5 months = $318 annual cooling
Heating (November–March):
- Monthly = (28,800 ÷ 10.5 × 12 × 30) ÷ 1,000 × $0.14
- = 987.4 kWh × $0.14
- = $138.24/month heating
- 5 months = $691 annual heating
- Total annual HVAC cost: ~$1,009 for the whole house
Worked Example 4: Garage Mini Split in Chicago
Setup: 24,000 BTU Senville (SEER2 17, HSPF2 8.5), Chicago electricity at $0.16/kWh. Garage used weekends + some evenings — averaging 4 hours/day cooling and 6 hours/day heating.
Cooling (June–August):
- Monthly = (24,000 ÷ 17 × 4 × 30) ÷ 1,000 × $0.16
- = 169.4 kWh × $0.16
- = $27.10/month cooling
- 3 months = $81 annual cooling
Heating (November–March):
- Monthly = (24,000 ÷ 8.5 × 6 × 30) ÷ 1,000 × $0.16
- = 508.2 kWh × $0.16
- = $81.32/month heating
- 5 months = $407 annual heating
- Total annual: ~$488 (part-time garage use only)
Running Cost by State: 12K BTU Mini Split (SEER2 20)
Here's what a 12,000 BTU mini split costs to run annually in every major state, accounting for both local electricity rates and typical cooling/heating seasons:
| State | Electricity Rate | Cooling Months | Heating Months | Annual Cooling | Annual Heating | Total Annual |
|---|---|---|---|---|---|---|
| Alabama | $0.14 | 6 | 4 | $121 | $91 | $212 |
| Arizona | $0.13 | 8 | 3 | $150 | $63 | $213 |
| California | $0.27 | 5 | 4 | $194 | $175 | $369 |
| Colorado | $0.15 | 4 | 6 | $86 | $146 | $232 |
| Connecticut | $0.30 | 4 | 6 | $173 | $291 | $464 |
| Florida | $0.15 | 9 | 2 | $194 | $49 | $243 |
| Georgia | $0.14 | 6 | 4 | $121 | $91 | $212 |
| Hawaii | $0.37 | 7 | 0 | $372 | $0 | $372 |
| Idaho | $0.10 | 3 | 6 | $43 | $97 | $140 |
| Illinois | $0.16 | 4 | 6 | $92 | $155 | $247 |
| Louisiana | $0.10 | 7 | 3 | $101 | $49 | $150 |
| Massachusetts | $0.28 | 4 | 6 | $161 | $272 | $433 |
| Minnesota | $0.15 | 3 | 7 | $65 | $170 | $235 |
| New York | $0.24 | 4 | 6 | $138 | $233 | $371 |
| Oregon | $0.12 | 3 | 5 | $52 | $97 | $149 |
| Texas | $0.14 | 7 | 3 | $141 | $68 | $209 |
| Virginia | $0.14 | 5 | 5 | $101 | $113 | $214 |
| Washington | $0.11 | 3 | 5 | $47 | $89 | $136 |
These are estimates for a single zone. Actual costs vary based on your home's insulation, thermostat settings, daily run hours, and weather extremes. Multi-zone systems multiply approximately by the number of active zones.
Running Cost Comparison: Mini Split vs. Alternatives
The real value of mini split running costs becomes clear when you compare to alternatives that serve the same purpose.
Annual Running Cost Comparison (Same 400 sq ft Room)
| System | Annual Cooling Cost | Annual Heating Cost | Total Annual | Savings vs. Mini Split |
|---|---|---|---|---|
| Mini split 12K (SEER2 20) | $144 | $186 | $330 | — |
| Window AC + baseboard heat | $288 | $648 | $936 | Mini split saves $606 |
| Portable AC + space heaters | $360 | $648 | $1,008 | Mini split saves $678 |
| Central AC + gas furnace | $216 | $240 | $456 | Mini split saves $126 |
| Central AC + electric furnace | $216 | $540 | $756 | Mini split saves $426 |
Assumptions: National average electricity at $0.17/kWh, natural gas at $1.50/therm, moderate climate (5 months cooling, 5 months heating), 8 hours/day cooling, 10 hours/day heating.
Cost Payback Period
The running cost savings from a mini split help offset the installation cost:
| Scenario | Installation Cost | Annual Savings | Payback Period |
|---|---|---|---|
| Replace window ACs + baseboard | $2,500 (DIY MrCool) | $606/year | 4.1 years |
| Replace window ACs + baseboard | $4,000 (pro Fujitsu) | $606/year | 6.6 years |
| Replace portable AC + space heaters | $2,500 (DIY MrCool) | $678/year | 3.7 years |
| Supplement central air (hot room) | $2,500 (DIY MrCool) | $200/year | 12.5 years |
| Replace electric furnace (heating) | $4,000 (pro Daikin) | $426/year | 9.4 years |
Best ROI scenario: If you're replacing window ACs plus electric baseboard heat (or space heaters), a mini split pays for itself in 3.7–6.6 years through electricity savings alone. After that, you're saving $500–$700 per year for the remaining 10–15 years of the unit's life — that's $5,000–$10,500 in lifetime savings.
How to Lower Your Monthly Mini Split Cost
These strategies can reduce your monthly running cost by 20–40%:
Raise cooling setpoint by 2–4°F. Moving from 72°F to 76°F saves approximately 8–16% on cooling costs. At $35/month, that's $3–$6/month savings. Most people acclimate within a week and don't notice the difference.
Use eco mode or sleep mode at night. These modes raise the setpoint by 1–2°F and reduce fan speed. Since your body naturally cools during sleep, you'll sleep just as comfortably while using 15–25% less electricity overnight.
Schedule run times. Don't cool an empty room. If you're at work from 9 AM to 5 PM, schedule the unit to power down at 9 and start pre-cooling at 4:30 PM. That eliminates 8 hours of daytime running — potentially halving your monthly cost.
Clean filters religiously. Dirty filters increase electricity consumption by 5–15%. If you pay $35/month, dirty filters add $1.75–$5.25/month — up to $63/year in wasted electricity for a maintenance task that takes 5 minutes.
Improve room insulation. Adding thermal curtains ($30–$80), weatherstripping ($10–$20), or window film ($50–$100) can reduce your cooling/heating load by 15–25%. The one-time investment of $90–$200 saves $40–$100 per year permanently.
Use ceiling fans. Running a ceiling fan (50 watts) creates a wind-chill effect that lets you raise the AC setpoint by 3–4°F without sacrificing comfort. The fan costs $0.20/day to run but saves $0.50–$1.00/day in AC costs.
Key Takeaways
- A 12K mini split costs $25–$75/month for cooling and $30–$100/month for heating depending on your electricity rate and climate
- Formula: Monthly cost = (BTU ÷ SEER2 × hours/day × 30) ÷ 1,000 × $/kWh
- Electricity rate is the biggest variable — the same unit costs $150/year in Louisiana but $464/year in Connecticut
- Mini splits save $600–$1,000/year compared to window AC + electric baseboard heat
- Payback period is 3.7–6.6 years when replacing window ACs and electric heat
- Raising your setpoint 2°F saves 6–10% on monthly costs
- Clean filters every 2–4 weeks to avoid wasting 5–15% on electricity