AC Tonnage Calculator
Find the right size air conditioner for your room or home
AC Sizing Reference Table
| Area (sq ft) | Tonnage | BTU/hr | kW |
|---|---|---|---|
| 150-250 | 1.0 ton | 12,000 | 3.5 kW |
| 250-400 | 1.5 ton | 18,000 | 5.3 kW |
| 400-600 | 2.0 ton | 24,000 | 7.0 kW |
| 600-900 | 3.0 ton | 36,000 | 10.6 kW |
| 900-1,200 | 4.0 ton | 48,000 | 14.1 kW |
| 1,200-1,500 | 5.0 ton | 60,000 | 17.6 kW |
AC Tonnage Calculation Methodology
This calculator uses industry-standard Manual J principles simplified for quick estimation. The calculation follows these steps:
Step 1: Calculate Room Volume
Volume (cubic feet) = Room Area (sq ft) × Ceiling Height (ft). This determines the total air volume that needs conditioning.
Step 2: Apply Base Cooling Load
Base BTU = Volume × 2.5 BTU/cu ft. This base factor accounts for the heat gain through walls, windows, and internal heat sources under standard conditions.
Step 3: Apply Climate Multiplier
The climate zone adjusts the base BTU for regional temperature differences:
| Climate Zone | States | Multiplier |
|---|---|---|
| Hot | FL, TX, AZ, NM, LA | 1.30 |
| Warm | CA, GA, NC, SC, AL | 1.15 |
| Moderate | NY, OH, VA, PA, IL | 1.00 |
| Cool | MN, MI, WA, OR, MT | 0.85 |
Step 4: Apply Sun Exposure Factor
- Direct Sun (1.10): South-facing or unshaded west-facing rooms with large windows
- Average (1.00): Standard exposure with partial shade
- Shaded (0.90): North-facing or heavily shaded by trees/structures
Step 5: Convert to Tonnage
Tonnage = Total BTU/hr ÷ 12,000. One ton of cooling equals 12,000 BTU/hr, which is the heat required to melt one ton of ice in 24 hours.
Note: This calculator provides a quick estimate for preliminary sizing. For precise HVAC design, a full ACCA Manual J calculation should be performed by a licensed HVAC contractor, which accounts for insulation values, window types, occupancy, equipment heat gain, and infiltration rates.
HVAC Sizing Guide
Proper AC sizing is critical for comfort, efficiency, and equipment longevity. Both undersizing and oversizing cause problems:
Problems with Oversizing
- Short cycling — the AC cools too quickly and shuts off, reducing dehumidification
- Higher humidity levels and reduced comfort
- Increased wear on compressor from frequent starts
- Higher upfront equipment cost
Problems with Undersizing
- Inability to maintain temperature during peak heat
- Continuous operation increases energy bills
- Premature equipment failure from constant running
- Hot spots and uneven cooling
SEER2 Efficiency Ratings
| SEER2 Rating | Efficiency Level | Typical Application |
|---|---|---|
| 14-16 | Standard | Budget installations, mild climates |
| 17-20 | High Efficiency | Most residential installations |
| 21+ | Ultra High Efficiency | Premium installs, hot climates, energy rebates |
Recommended HVAC Products
Based on your AC tonnage calculation, PES Supply offers these compatible products:
SolarEdge HVAC Offset Systems
Grid-tie solar systems designed to offset HVAC energy consumption
View SystemsNeed help matching an AC unit to a solar + storage system? Contact our technical team for system design support.
AC Sizing for Solar-Powered Systems
If you plan to run your AC on solar power, additional considerations apply:
- Inverter sizing: AC inverter compressors require 3-5x running wattage for startup surge
- Battery capacity: A 1-ton AC draws ~1.2 kW — running 8 hours requires ~10 kWh of battery storage
- Solar panel offset: 1 ton of AC for 8 hours/day needs ~3-4 kW of solar to offset consumption
- Hybrid inverters: Sol-Ark and EG4 hybrid inverters can manage AC loads with solar + battery seamlessly
Use our Battery Backup Runtime Calculator and Amps to kW Calculator for complementary sizing calculations.
Need Help Sizing Your System?
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