How it works
Estimate BTU requirement for heating or cooling a room.
Input query strings and outputs
Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.
Input query strings
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?length=Length (ft)Number · Optional · Default: 20
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?width=Width (ft)Number · Optional · Default: 15
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?ceilingHeight=Ceiling Height (ft)Number · Optional · Default: 8
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?insulation=InsulationText · Optional · Default: average
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?sunExposure=Sun ExposureText · Optional · Default: average
Outputs
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resultResultText · Primary output
result contains the calculator’s complete rendered result area, including its visible result cards, tables, charts, and messages.
Estimate the heating and cooling power needed for a room
Description
The BTU Calculator (British Thermal Units) is an HVAC planning tool that helps you choose the right air conditioner or heater for a room. Buying a unit that is too small won’t cool the room, while one that is too large will cycle on and off too quickly, wasting energy. This tool considers room dimensions, ceiling height, insulation quality, and sun exposure to provide a tailored energy estimate.
Inputs
- Room Dimensions:
- Length & Width (ft): The floor area.
- Ceiling Height (ft): Standard is 8ft; higher ceilings require more power.
- Insulation: Choose from Good, Average, or Poor.
- Sun Exposure: Choose from Shaded, Average, or Sunny.
Outputs
- Estimated BTUs: The total power requirement needed for the space.
Chart
- N/A: This tool provides a direct numeric energy requirement.
“Good to Know”
- The “20 BTU” Rule: A basic rule of thumb is that you need about 20 BTUs per square foot of living space.
- Ceiling Height: For every foot of ceiling height over 8 feet, you should generally add 10% more power to your calculation.
- Sun & Shade: A very sunny room requires about 10% more cooling power than an average room, while a heavily shaded room can get by with 10% less.
Examples
Example 1: Standard Bedroom
- Input: 15x15 ft, 8ft ceiling, Avg Insulation
- Output: 4,500 BTU
Example 2: Large Sunny Living Room
- Input: 20x25 ft, 10ft ceiling, Sunny, Poor Insulation
- Output: 14,300 BTU
Example 3: Shaded Office
- Input: 10x10 ft, 8ft ceiling, Shaded, Good Insulation
- Output: 1,620 BTU