BTU Calculator
Calculate heating and cooling BTU requirements based on room size, insulation, and climate.
A BTU calculator estimates the heating or cooling capacity needed for a room based on its size, insulation, sun exposure, and occupancy.
Examples
300 sq ft room, cooling
Frequently Asked Questions
What is a BTU?
How do I convert BTU to tons?
Quick Tips
- •Oversize your unit slightly rather than undersizing; an undersized system runs constantly and wastes energy.
- •Have a professional perform a Manual J load calculation for whole-home HVAC sizing.
- •Consider zoned systems for homes with rooms that have very different heating and cooling needs.
A BTU calculator estimates the heating or cooling capacity needed for a room based on its size, insulation, sun exposure, and occupancy.
How to Use This Calculator
Select heating or cooling mode, enter your room size in square feet, ceiling height, insulation quality, sun exposure, and the number of occupants. The calculator estimates the BTU (British Thermal Units) per hour needed.
Understanding the Formula
Base BTU = Room Sq Ft x Rate (20 BTU/sq ft for cooling, 30 for heating). Adjustments are applied for ceiling height, insulation quality, sun exposure, and additional occupants (600 BTU per extra person beyond 2).
Examples
300 sq ft room, cooling
Base: 300 x 20 = 6,000 BTU. With average insulation, medium sun, standard ceiling, and 2 occupants: 6,000 BTU/hr (0.5 tons).
Frequently Asked Questions
What is a BTU?
A British Thermal Unit (BTU) is the amount of energy needed to heat or cool one pound of water by one degree Fahrenheit. Air conditioners and heaters are rated in BTU/hr to indicate their capacity.
How do I convert BTU to tons?
One ton of air conditioning equals 12,000 BTU/hr. Divide the BTU requirement by 12,000 to get the tonnage needed.
Assumptions & Limitations
- Uses simplified rule-of-thumb factors (20 BTU/sq ft for cooling, 30 for heating); a professional Manual J calculation is more precise.
- Does not account for climate zone, number of windows, or heat-generating appliances in the room.
- Insulation quality is a broad estimate; actual R-values vary by wall, ceiling, and floor construction.