AC Sizing Calculator
Calculate the right air conditioner size for your home using simplified Manual J method. Compare SEER ratings and estimate annual cooling costs.
Generally, you need 1 ton of cooling capacity per 400-600 sq ft depending on climate, insulation, and other factors. This calculator uses a simplified Manual J approach for more accuracy.
About This Calculator
Choosing the right air conditioner size is crucial for home comfort and energy efficiency. An undersized AC will run constantly and struggle on the hottest days, while an oversized unit short-cycles, wastes energy, and fails to properly control humidity. Our AC Sizing Calculator uses a simplified Manual J approach to estimate the correct tonnage for your home based on square footage, climate zone, insulation quality, ductwork condition, and other key factors.
2026 HVAC Market Update: Central AC systems cost $5,000-$12,000 installed depending on size and efficiency. The transition to SEER2 ratings and R-454B refrigerant has increased equipment costs 8-12% compared to 2024. Minimum efficiency is now 13.4 SEER2 in the North and 14.3 SEER2 in the South/Southwest. Heat pumps have become cost-competitive with AC systems while providing both heating and cooling, making them an increasingly popular choice.
The federal tax credit for high-efficiency AC (17+ SEER2) expired December 31, 2025, but heat pump tax credits of $2,000 remain available through 2032. This calculator helps you determine correct sizing and compare efficiency options to find the best balance of comfort, cost, and long-term value.
Trusted Sources
How to Use the AC Sizing Calculator
- 1Enter your home's total conditioned square footage (heated/cooled living space).
- 2Select the number of stories—upper floors and vaulted ceilings need more cooling capacity.
- 3Choose your climate zone based on geographic location (affects design temperature).
- 4Specify home characteristics: insulation quality, window type, and sun exposure.
- 5In advanced mode, add factors for ductwork condition, age of home, and occupancy.
- 6Select SEER2 rating to compare energy efficiency options and annual operating costs.
- 7Review the recommended tonnage range and see how different efficiencies affect your costs.
- 8Use results as a starting point—get professional Manual J calculation for final sizing.
2026 Central AC and Heat Pump Costs
Current pricing for residential cooling systems has increased due to new efficiency standards and refrigerant transitions.
Central AC System Costs (Installed):
| Size | Equipment | Installation | Total Installed |
|---|---|---|---|
| 1.5 ton | $1,800-2,800 | $2,500-4,000 | $4,300-6,800 |
| 2 ton | $2,200-3,400 | $2,700-4,200 | $4,900-7,600 |
| 2.5 ton | $2,600-4,000 | $2,900-4,500 | $5,500-8,500 |
| 3 ton | $3,000-4,600 | $3,100-4,800 | $6,100-9,400 |
| 3.5 ton | $3,400-5,200 | $3,300-5,100 | $6,700-10,300 |
| 4 ton | $3,800-5,800 | $3,500-5,400 | $7,300-11,200 |
| 5 ton | $4,500-7,000 | $3,800-5,800 | $8,300-12,800 |
Heat Pump Costs (Installed):
| Size | Equipment | Installation | Total Installed |
|---|---|---|---|
| 2 ton | $2,800-4,200 | $3,000-4,500 | $5,800-8,700 |
| 2.5 ton | $3,200-4,800 | $3,200-4,800 | $6,400-9,600 |
| 3 ton | $3,600-5,400 | $3,400-5,200 | $7,000-10,600 |
| 4 ton | $4,400-6,600 | $3,800-5,800 | $8,200-12,400 |
| 5 ton | $5,200-8,000 | $4,200-6,400 | $9,400-14,400 |
Cost by Efficiency Level:
| SEER2 Rating | Price Premium | Best For |
|---|---|---|
| 13.4-14.3 (minimum) | Base price | Cold climates, budget |
| 15-16 | +$500-1,000 | Moderate climates |
| 17-18 | +$1,000-2,000 | Hot climates |
| 19-21 | +$2,000-3,500 | Maximum efficiency |
| 22+ (variable) | +$3,500-6,000 | Premium comfort/efficiency |
2026 Tax Credit Status:
- AC tax credit (25C): Expired December 31, 2025
- Heat pump tax credit: $2,000 maximum through 2032
- State/utility rebates: Vary by location, check DSIRE database
Understanding AC Size Ratings
Air conditioning capacity is measured in multiple ways:
Tons of Cooling
- 1 ton = 12,000 BTU/hour of cooling capacity
- Named after ice: melting 1 ton of ice over 24 hours absorbs 12,000 BTU/hr
- Residential systems: 1.5 to 5 tons typical
- Common sizes: 1.5, 2, 2.5, 3, 3.5, 4, 5 tons (half-ton increments)
BTU (British Thermal Units)
- Measures heat removal capacity per hour
- Higher BTU = more cooling capacity
- Window units rated directly in BTU (5,000-25,000)
- Central systems rated in tons (multiply by 12,000 for BTU)
General Sizing Guidelines:
| Home Size (sq ft) | Cool Climate | Moderate | Hot/Humid |
|---|---|---|---|
| 800-1,000 | 1.5 tons | 1.5-2 tons | 2 tons |
| 1,000-1,300 | 2 tons | 2-2.5 tons | 2.5 tons |
| 1,300-1,600 | 2.5 tons | 2.5-3 tons | 3 tons |
| 1,600-1,900 | 3 tons | 3-3.5 tons | 3.5 tons |
| 1,900-2,200 | 3.5 tons | 3.5-4 tons | 4 tons |
| 2,200-2,600 | 4 tons | 4-4.5 tons | 4.5-5 tons |
| 2,600-3,200 | 4.5-5 tons | 5 tons | 5+ tons |
These are general guidelines. Actual sizing depends on insulation, windows, orientation, and occupancy.
Capacity vs. Nominal Size: Actual capacity varies with outdoor temperature. A "3-ton" unit delivers:
- 36,000 BTU at 95°F outdoor
- 34,000 BTU at 100°F outdoor
- 31,000 BTU at 105°F outdoor
- 28,000 BTU at 110°F outdoor
SEER2 Ratings and 2026 Efficiency Standards
SEER2 (Seasonal Energy Efficiency Ratio 2) is the current efficiency standard, replacing SEER in 2023.
SEER vs. SEER2:
- SEER2 tests under higher static pressure (more realistic conditions)
- SEER2 ratings are approximately 4-5% lower than equivalent SEER
- A 16 SEER unit = approximately 15.2 SEER2
- Always compare same rating type (SEER2 to SEER2)
2026 Minimum Efficiency by Region:
| Region | AC Minimum | Heat Pump Minimum |
|---|---|---|
| North (Zone 1-3) | 13.4 SEER2 | 14.3 SEER2, 7.5 HSPF2 |
| South (Zone 4+) | 14.3 SEER2 | 14.3 SEER2, 7.5 HSPF2 |
| Southwest | 14.3 SEER2, 11.7 EER2 | 14.3 SEER2, 7.5 HSPF2 |
Annual Cost Comparison (3-ton system, $0.15/kWh, 1,500 cooling hours):
| SEER2 | Annual kWh | Annual Cost | Savings vs Min |
|---|---|---|---|
| 13.4 | 4,030 | $605 | — |
| 14.3 | 3,776 | $566 | $39/year |
| 16 | 3,375 | $506 | $99/year |
| 18 | 3,000 | $450 | $155/year |
| 20 | 2,700 | $405 | $200/year |
| 22 | 2,455 | $368 | $237/year |
SEER2 Selection Guide:
| Climate/Usage | Recommended | Why |
|---|---|---|
| Cold climate (<800 hrs AC) | 13.4-14.3 | Short payback unlikely |
| Moderate (800-1,500 hrs) | 15-17 | Good balance |
| Hot climate (1,500-2,500 hrs) | 17-20 | Fast payback |
| Very hot (2,500+ hrs) | 20+ | Maximum savings |
| Plan to stay 5+ years | Higher tier | Time for payback |
| Selling soon | Minimum code | Lower upfront cost |
Manual J Load Calculation Explained
Professional HVAC contractors use Manual J calculations from ACCA for accurate sizing.
What Manual J Considers:
1. Building Envelope:
- Wall insulation R-values (R-13 to R-21 typical)
- Ceiling/attic insulation (R-30 to R-60)
- Foundation type and insulation
- Air infiltration rate (blower door tested or estimated)
- Window U-factor, SHGC, and area by orientation
2. Heat Sources (Sensible + Latent):
- Solar heat gain by window orientation and shading
- Internal gains (appliances, lighting, people)
- Occupancy (1-2 people per bedroom typical)
- Equipment heat (computers, TVs, etc.)
3. Climate Data:
- Design outdoor temperature (1% cooling design day)
- Indoor design temperature (typically 75°F)
- Humidity levels (affects latent load)
- Solar radiation by orientation
4. Duct System:
- Location (conditioned space, attic, crawlspace)
- Insulation level (R-4 to R-8 typical)
- Leakage rate (typically 5-25%)
- Adds load if ducts are in unconditioned space
Manual J Output:
- Sensible cooling load (heat removal, BTU/hr)
- Latent cooling load (moisture removal, BTU/hr)
- Total cooling load (sensible + latent)
- Recommended equipment capacity (tons)
Simplified vs. Full Manual J:
| Aspect | Simplified (This Calculator) | Full Manual J |
|---|---|---|
| Accuracy | ±15-20% | ±5-10% |
| Time required | 2 minutes | 1-3 hours |
| Cost | Free | $100-400 |
| Best for | Preliminary sizing, comparison | Final equipment selection |
| Software | Simplified factors | Wrightsoft, CoolCalc, etc. |
When to Get Professional Manual J:
- New construction (often required by code)
- Homes over 3,000 sq ft
- Unusual construction or layout
- Major insulation/window upgrades
- Zoned systems or multiple units
- Heat pump installations
Heat Pump vs. Central AC Comparison
Heat pumps provide both heating and cooling, making them increasingly popular.
Cost Comparison:
| Factor | Central AC | Heat Pump |
|---|---|---|
| Equipment (3 ton) | $3,000-4,600 | $3,600-5,400 |
| Installation | $3,100-4,800 | $3,400-5,200 |
| Total installed | $6,100-9,400 | $7,000-10,600 |
| Premium for HP | — | +$900-1,200 |
| Tax credit (2026) | None | Up to $2,000 |
| Net cost difference | — | Often lower with credit |
Operating Cost Comparison:
| Scenario | AC + Gas Furnace | Heat Pump Only |
|---|---|---|
| Cooling cost (same) | $400-800/year | $400-800/year |
| Heating cost | $600-1,500/year (gas) | $400-1,000/year |
| Total annual | $1,000-2,300 | $800-1,800 |
| Savings with HP | — | 15-35% typical |
Heat pump savings depend on climate, electricity rates, and gas rates.
When Heat Pumps Make Sense:
- Moderate climates (mild winters)
- High gas prices, low electricity prices
- New construction (design for HP from start)
- Replacing both AC and furnace
- Federal tax credit eligibility
- Environmental preference (no combustion)
When AC + Furnace Makes Sense:
- Very cold climates (below 0°F common)
- Very low gas prices
- Existing efficient furnace
- Replacing only AC (not furnace)
- Limited electrical service capacity
Cold Climate Heat Pumps: Modern cold-climate heat pumps (ccASHP) maintain heating efficiency down to -15°F to -25°F, making them viable even in northern states. Look for units with:
- HSPF2 rating of 9+ (higher is better)
- Rated heating capacity at low temperatures
- Variable-speed compressor technology
- Cold climate rating (specific models)
Common Sizing Mistakes to Avoid
Many homes have improperly sized air conditioners. Here is what to avoid:
Mistake 1: Bigger Is Better
- Oversized AC short-cycles (runs briefly, shuts off)
- Poor humidity control—house feels clammy
- Uneven temperatures room-to-room
- Higher energy bills from inefficient cycling
- Reduced equipment lifespan from frequent starts
- Uncomfortable cold blasts then warm periods
Mistake 2: Matching the Old System
- Previous system may have been wrong-sized
- Home insulation improvements reduce load
- New windows dramatically change requirements
- Duct repairs may have been made
- Always recalculate for replacements
Mistake 3: Using Only Square Footage
- Ignores insulation quality (R-13 vs R-21 walls)
- Misses ductwork location and condition
- Does not account for climate differences
- Window area and type matters significantly
- Ceiling height affects volume to cool
Mistake 4: Ignoring Ductwork
- Leaky ducts waste 20-30% of cooling capacity
- Undersized ducts restrict airflow
- Poorly insulated attic ducts add load
- Fix ducts BEFORE sizing equipment
- Duct problems make any system underperform
Mistake 5: Not Considering Humidity
- Properly sized units run longer, remove more moisture
- Oversized units cool quickly but leave humid air
- In humid climates (FL, TX coast, Southeast), right-sizing is critical
- Consider two-stage or variable-speed for humid climates
Rule of Thumb Check: As a rough verification, divide square footage by climate factor:
- Hot/humid climates: 350-400 SF per ton
- Moderate climates: 450-500 SF per ton
- Cool climates: 550-650 SF per ton
Example: 2,000 SF in Houston: 2,000 ÷ 400 = 5 tons Example: 2,000 SF in Chicago: 2,000 ÷ 550 = 3.6 tons (use 3.5)
Variable-Speed and Two-Stage Systems
Advanced compressor technology provides better comfort and efficiency.
Single-Stage (On/Off):
- Runs at 100% or not at all
- Least expensive option
- Adequate for mild climates
- May short-cycle if oversized
- Typical efficiency: 13.4-18 SEER2
Two-Stage:
- Runs at ~60-65% or 100%
- Better humidity control
- More even temperatures
- Quieter at low stage
- 15-30% more efficient in real use
- Cost: $500-1,500 premium
- Typical efficiency: 16-20 SEER2
Variable-Speed (Inverter):
- Runs at 25-100% as needed
- Best humidity control
- Most even temperatures
- Whisper-quiet operation
- 30-50% more efficient in real use
- Cost: $2,000-4,000 premium
- Typical efficiency: 18-26 SEER2
Sizing Differences:
| Type | Sizing Approach | Tolerance |
|---|---|---|
| Single-stage | Size exactly to load | Minimal oversizing |
| Two-stage | Slightly generous OK | +0.5 ton acceptable |
| Variable-speed | Generous sizing OK | +1 ton acceptable |
Best Applications:
| Situation | Recommended Type |
|---|---|
| Budget-focused | Single-stage |
| Humid climates | Two-stage or variable |
| Maximum efficiency | Variable-speed |
| Sensitive to noise | Variable-speed |
| Zoned systems | Variable-speed |
| Extreme temperature swings | Two-stage or variable |
| Simple replacement | Match existing type |
Climate Zones and Design Temperatures
Your climate zone determines minimum efficiency requirements and affects sizing.
IECC Climate Zones:
| Zone | States | Design Temp (°F) | Cooling Hours |
|---|---|---|---|
| 1 | S. Florida, Hawaii | 91-95 | 3,000-4,000+ |
| 2 | Gulf Coast, S. Texas, Arizona | 95-105 | 2,000-3,500 |
| 3 | California, NC, TN, OK | 92-100 | 1,200-2,500 |
| 4 | KS, KY, VA, NJ | 90-95 | 800-1,500 |
| 5 | CO, IN, PA, NY | 88-92 | 600-1,200 |
| 6 | MT, WI, ME, NH | 85-90 | 400-800 |
| 7 | MN, ND, WY | 85-88 | 300-600 |
Design Temperature Explained: The outdoor design temperature is exceeded only 1% of hours (about 88 hours/year). Systems are sized for this temperature, not the absolute maximum.
Impact on Sizing:
| Design Temp | SF per Ton Factor |
|---|---|
| 100°F+ | 300-350 |
| 95-100°F | 350-400 |
| 90-95°F | 400-450 |
| 85-90°F | 450-500 |
| Below 85°F | 500-600 |
Humidity Considerations: High humidity requires additional latent cooling capacity:
- Dry climates (AZ, NV): Primarily sensible load
- Moderate (most of US): Mixed sensible/latent
- Humid (FL, LA, TX coast): High latent load
In humid climates:
- Avoid oversizing (causes humidity problems)
- Consider two-stage or variable-speed
- Ensure adequate run time for dehumidification
- May need supplemental dehumidifier in extreme cases
Ductwork Considerations
Ductwork significantly impacts AC performance and proper sizing.
Duct Leakage Impact:
| Leakage Rate | Effective Capacity | Cost Impact |
|---|---|---|
| 5% (tight) | 95% of rated | Minimal |
| 15% (average) | 85% of rated | 15% higher bills |
| 25% (leaky) | 75% of rated | 30% higher bills |
| 35%+ (poor) | 65% of rated | 40%+ higher bills |
A 3-ton system with 25% leakage delivers only 2.25 tons to the house.
Duct Location Impact:
| Location | Temperature Gain | Load Impact |
|---|---|---|
| Conditioned space | None | Optimal |
| Vented crawlspace | 5-10°F | +10-15% load |
| Attic (insulated R-8) | 10-15°F | +15-25% load |
| Attic (uninsulated) | 20-30°F | +25-40% load |
When to Address Ducts First:
- Duct leakage exceeds 15%
- Ducts in unconditioned attic are uninsulated
- Rooms have very uneven temperatures
- System seems to run constantly
- Previous oversizing may have masked duct issues
Duct Improvement Costs:
| Service | Typical Cost | Energy Savings |
|---|---|---|
| Duct sealing (mastic) | $300-600 | 10-20% |
| Professional duct sealing | $1,000-2,500 | 15-30% |
| Duct insulation (R-8) | $500-1,500 | 5-15% |
| Full duct replacement | $3,000-7,000 | 20-40% |
Duct Sizing Basics: Undersized ducts restrict airflow, causing:
- Reduced capacity (system works harder)
- Higher static pressure
- Increased energy use
- Noise from high-velocity air
- Premature equipment failure
General guidelines:
- 400 CFM per ton of cooling
- Supply: 1 SF duct per 150 CFM
- Return: 1 SF duct per 100 CFM (larger)
Pro Tips
- 💡Fix ductwork issues BEFORE replacing AC—leaky or undersized ducts can waste 20-30% of cooling and may have caused your old system to seem undersized.
- 💡Consider a heat pump instead of AC-only—the $2,000 federal tax credit (through 2032) often makes heat pumps cheaper than equivalent AC systems.
- 💡Get at least three quotes that include Manual J calculations—compare methodologies and assumptions, not just bottom-line prices.
- 💡Do not automatically match your old system size—homes often have been improved (insulation, windows) and may need less capacity now.
- 💡In humid climates (FL, Gulf Coast, Southeast), avoid oversizing—proper sizing ensures adequate run time for dehumidification.
- 💡Variable-speed systems are worth the premium in hot climates, humid areas, and homes where someone is present during the day.
- 💡Ask about ENERGY STAR certification—these units meet strict efficiency guidelines and may qualify for utility rebates.
- 💡The indoor coil (evaporator) must match the outdoor unit—mismatched components reduce efficiency below rated SEER2.
- 💡Consider system age and condition together—a 15-year-old system with expensive repairs often makes replacement the better investment.
- 💡Smart thermostats can improve comfort and efficiency with any system—they learn your patterns and optimize run times.
- 💡Schedule installation during spring or fall for better pricing and availability—summer emergencies cost 10-20% more.
- 💡Check utility rebate programs before purchasing—many offer $200-500 for high-efficiency systems, reducing payback time.
Frequently Asked Questions
A 3-ton (36,000 BTU) air conditioner typically cools 1,500-1,800 square feet in average conditions. However, this varies significantly based on climate, insulation, windows, and ceiling height. In Phoenix, 3 tons might cool only 1,200-1,400 sq ft due to extreme heat, while in Minneapolis it could handle 1,800-2,200 sq ft. Use our calculator with your specific factors for accurate sizing.
