BTU Calculator
Calculate heating and cooling BTU requirements for your space. Get AC tonnage and furnace sizing recommendations.
How to Use This Calculator
Properly sizing your HVAC system is crucial for comfort and energy efficiency. An undersized unit will run constantly and never reach the desired temperature, while an oversized unit will cycle too frequently, wasting energy and failing to dehumidify properly.
- Measure the room or space length and width in feet. For multiple rooms, calculate each separately.
- Enter the ceiling height (standard is 8 feet, but many homes have 9-10 foot ceilings).
- Select your climate zone - this significantly affects both heating and cooling needs.
- Rate your insulation quality - older homes typically have average to poor insulation.
- Add details about sun exposure, windows, occupants, and whether it includes a kitchen.
Why This Matters
HVAC systems represent one of the largest energy expenses in a home, and proper sizing can reduce energy costs by 20-40%. An oversized AC cools quickly but shuts off before properly dehumidifying, leaving you with a cold, clammy space. An undersized unit runs constantly, increasing wear and energy bills while never achieving comfort.
- Calculate cooling BTU for air conditioning sizing
- Determine heating BTU for furnace selection
- Get AC tonnage recommendations for central systems
- Find window AC unit size recommendations
- Account for climate, insulation, and usage factors
Worked Examples
Master Bedroom
A 14' x 16' bedroom with 8-foot ceilings, average insulation, 2 windows, in a moderate climate.
Living Room in Hot Climate
A 20' x 25' living room with high ceilings, south-facing windows, in Arizona.
Whole House Calculation
2,000 sq ft home in cold climate with average insulation.
Common Mistakes to Avoid
- Using square footage alone - ceiling height, windows, and insulation significantly affect BTU needs.
- Ignoring climate zone - a Florida home needs different sizing than one in Minnesota.
- Oversizing the system - bigger is not better for HVAC; it causes short cycling and humidity issues.
- Forgetting heat sources - kitchens, electronics, and extra occupants add significant heat load.
- Not accounting for ductwork - even a properly sized unit performs poorly with inadequate ducts.