About the HVAC Load Calculator
What is the HVAC Load Calculator?
Choosing AC tonnage by floor area alone often gets it wrong. This calculator estimates the room's heat load from its walls and roof, occupants, sun through windows, appliances and lighting, adds a 10% margin and picks a standard AC size.
Top-floor and west-facing rooms in Indian summers need noticeably more cooling.
How to use the HVAC Load Calculator
- Room Floor Area (m²) (sample: 14)
- Ceiling Height (m) (sample: 3)
- Room Exposure (sample: Intermediate floor, shaded walls)
- Usual Occupants (sample: 2)
- Sun-Facing Window Area (m²) (sample: 2)
- Heat from Appliances – TV, PC, fridge (W) (sample: 300)
- Press Calculate AC Size (results also refresh as you type). The result card shows the Recommended AC Size, along with Cooling load, Cooling load in tons and Cooling load in BTU/h.
Formula used
Cooling load = (Envelope + People + Windows + Appliances + Lighting) × 1.1
- Envelope = floor area × 100 W/m² (140 W/m² for top floors or west walls), scaled for ceiling height
- People = 120 W each
- Tons = watts ÷ 3,517
A rule-of-thumb estimate; large or glass-heavy spaces need a detailed heat-load calculation.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Room Floor Area (m²) | 14 |
| Ceiling Height (m) | 3 |
| Room Exposure | Intermediate floor, shaded walls |
| Usual Occupants | 2 |
| Sun-Facing Window Area (m²) | 2 |
| Heat from Appliances – TV, PC, fridge (W) | 300 |
| Result | Value |
|---|---|
| Recommended AC Size | 1 ton |
| Cooling load | 2,917 W |
| Cooling load in tons | 0.83 TR |
| Cooling load in BTU/h | 9,954 BTU/h |
Tips for using the HVAC Load Calculator
- Shade west windows and insulate the roof to cut the load by a fifth or more.
- An inverter AC handles varying loads more efficiently than a fixed-speed one.