Formula Used
Area: floor area = length × width
Volume: volume = length × width × height
Conduction: Q = U × A × ΔT
Airflow from leakage: CFM = volume × ACH ÷ 60
Sensible air load: Q = 1.08 × CFM × ΔT
Latent humidity load: Q = 0.68 × CFM × grains difference
Electric gains: Btu/hr = watts × 3.412
Solar gain: Q = window area × solar gain × shading factor
Cooling tons: tons = total cooling Btu/hr ÷ 12,000
How to Use This Calculator
Enter the room length, width, height, and opening areas. Select the measurement units first.
Enter indoor and outdoor design temperatures for both seasons.
Add U-values for walls, roof, floor, windows, and doors.
Enter air changes, people, lights, equipment, solar gain, and humidity data.
Press calculate. The result appears above the form and below the header.
Use CSV or PDF buttons to save the report.
Example Data Table
| Input |
Example value |
Meaning |
| Room size |
20 ft × 15 ft × 10 ft |
Defines area and air volume. |
| Cooling temperatures |
95°F outside, 75°F inside |
Sets cooling temperature difference. |
| Heating temperatures |
25°F outside, 70°F inside |
Sets heating temperature difference. |
| Air changes |
0.50 ACH |
Estimates infiltration airflow. |
| Internal loads |
2 people, 600 W lights, 800 W equipment |
Adds room heat gains. |
About Cooling and Heating Load Calculation
A cooling and heating load calculation estimates the heat a room gains or loses during design conditions. It helps select air conditioners, heat pumps, furnaces, ducts, and vents. This calculator uses room size, construction U values, air changes, people, lighting, equipment, solar gain, and humidity data.
Why This Load Matters
A unit that is too small may run nonstop. It may not reach the selected indoor temperature. A unit that is too large can short cycle. It may remove less moisture and waste energy. A balanced estimate gives a better starting point for comfort planning.
Main Load Sources
Conduction is heat flow through walls, roof, floor, windows, and doors. It depends on surface area, U value, and temperature difference. Ventilation and leakage add outdoor air load. Cooling also includes solar heat through windows. People, lights, and equipment add sensible heat. Moisture adds latent cooling load.
Heating and Cooling Differences
Cooling design includes indoor gains because they increase room heat. It also includes solar radiation and latent humidity load. Heating design is usually conservative. Many designers do not subtract internal gains unless a steady process proves them reliable. This tool includes a credit field, so you can decide the amount.
Using Results Wisely
The final values are shown in Btu per hour, tons of cooling, and kilowatts. The tons value helps compare air conditioner size. The area load helps check whether the number seems realistic. Very high values may show poor insulation, large glass area, high leakage, or extreme design weather.
Design Notes
This calculator is a planning tool, not a replacement for a certified Manual J or engineered report. Real buildings have thermal mass, orientation, shading, duct losses, occupancy schedules, and local code rules. Use accurate measurements when possible. Enter conservative outdoor design temperatures. Check manufacturer data before buying equipment. For final installation, ask a qualified professional to verify the load, equipment match, airflow, duct capacity, and safety requirements.
Advanced Options
Advanced fields improve control. You can add extra outdoor air, change safety factor, enter grain difference, and adjust supply air temperature rise. These options help compare tight rooms, leaky rooms, shaded rooms, and sun exposed rooms under the same calculation method before sizing.
FAQs
What is a heating load?
A heating load is the heat needed to keep a room warm during cold outdoor conditions. It includes heat lost through surfaces and outdoor air leakage.
What is a cooling load?
A cooling load is the heat that must be removed from a room. It includes conduction, ventilation, solar gain, people, lighting, equipment, and moisture.
What does U-value mean?
U-value shows how easily heat passes through a building surface. A lower U-value means better insulation and a smaller conduction load.
Why does cooling include latent load?
Latent load comes from moisture. Air conditioners must remove water vapor as well as heat, especially in humid climates.
What is ACH?
ACH means air changes per hour. It estimates how many times room air is replaced by outdoor air in one hour.
Why is a safety factor used?
A safety factor adds a margin for uncertain inputs, leakage, solar exposure, or future changes. Too much margin can oversize equipment.
Can this replace a professional design?
No. It is a planning calculator. Final equipment selection should follow local codes, manufacturer data, and a professional load study.
Why are results shown in tons?
Cooling equipment is often rated in tons. One cooling ton equals 12,000 Btu per hour.