BTU / HVAC Sizing Calculator

Calculate the BTU capacity needed for heating and cooling based on room size, insulation, climate, and windows.

Inputs

Room Area

sq ft

Ceiling Height

Insulation Quality

Climate Zone

Number of Windows

Tab to move between fields

Results

Cooling BTU Needed

11,800

AC Tonnage1

Suggested AC Size1 tons

Furnace BTU12,980

BTU per Sq Ft29.5

How to Use This Calculator

Enter the Room Area (sq ft) and Ceiling Height (ft).
Select Insulation Quality (Poor, Average, Good, or Excellent) for the space.
Choose the Climate Zone that matches your location.
Review the recommended BTU capacity for both heating and cooling.
Use the output to select the right window AC, mini-split, or furnace for the room.

How the result changes with Room Area

Room Area	Cooling BTU Needed
1,045	25,990
3,533	80,726
6,518	146,396
9,005	201,110

What each input means

Room Area: Total floor area of the room or space to condition.
Ceiling Height: Height of the ceiling in feet.
Insulation Quality: Quality of wall and ceiling insulation in the space.
Climate Zone: General climate zone for your location.
Number of Windows: Number of windows in the room (adds ~1000 BTU each).

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Room Area = 400, Ceiling Height = 8, Insulation Quality = 2, Climate Zone = 2 = 5 input(s) provided
Calculate Cooling BTU Needed
Cooling BTU Needed
11800 = 11800
Calculate AC Tonnage
AC Tonnage
1 = 1
Calculate Suggested AC Size
Suggested AC Size
1 = 1

Engine last updated July 11, 2026. Checked against 3 independently-derived tests — how we verify calculators.

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