HVAC Load Calculator (BTU Estimator)
Calculate the required cooling and heating capacity for your space.
How to Calculate Your HVAC Needs
Choosing the right size for your Air Conditioning or Heating system is critical for energy efficiency and comfort. A unit that is too small won't cool the room properly on hot days, while an oversized unit will "short cycle," turning on and off too frequently, which increases wear and tear and fails to dehumidify the air.
The BTU Formula Used
This calculator uses the industry-standard Manual J logic simplified for residential use:
- Base Area Calculation: (Width × Length) × 20 BTU per square foot.
- Ceiling Adjustment: If ceilings are higher than 8 feet, the volume increase is accounted for.
- Occupancy: We add 600 BTUs for every person who regularly occupies the space beyond the first two people.
- Kitchen Factor: Cooking appliances generate significant heat. If the space is a kitchen, we add 4,000 BTUs to the total.
- Insulation & Sun: We apply multipliers (0.8x to 1.25x) based on how well the room retains temperature and how much direct sunlight it receives.
Typical BTU Chart by Square Footage
| Square Footage | Required BTU Capacity | Tons |
|---|---|---|
| 100 – 150 sq ft | 5,000 BTU | 0.4 Tons |
| 250 – 350 sq ft | 8,000 BTU | 0.7 Tons |
| 450 – 550 sq ft | 12,000 BTU | 1.0 Tons |
| 700 – 1,000 sq ft | 18,000 BTU | 1.5 Tons |
| 1,200 – 1,500 sq ft | 24,000 BTU | 2.0 Tons |
Why "Tons" Matter
In the HVAC industry, capacity is often measured in "Tons." This doesn't refer to the weight of the machine. One ton of air conditioning is defined as the ability to remove 12,000 BTUs of heat per hour. Therefore, a 3-ton unit is capable of moving 36,000 BTUs.
Frequently Asked Questions
What happens if I buy a unit that is too large?
An oversized unit will cool the room very quickly but will shut off before it has a chance to remove humidity. This leaves the room feeling "cold and clammy" and leads to higher electricity bills due to the high starting current of the compressor.
Do windows affect the calculation?
Yes. Our "Sun Exposure" toggle helps account for this. If you have large floor-to-ceiling windows facing south, you should select "Very Sunny" to ensure you have enough cooling power to offset the solar heat gain.