Furnace BTU Size Calculator

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Calculates the appropriate furnace BTU size based on square footage and climate conditions.

How To Use

How to use this calculator

Start with your values, or try a preset.

Step 1

Enter Home Square Footage (sq ft), Climate Zone, and Insulation Quality in the units shown.

Step 2

Read Estimated BTU Requirement and Recommended Furnace Size in the results panel. Results update as you change the inputs.

Step 3

Choose a preset to load an example, then adjust the values for your situation.

Worked Examples

See the inputs and their calculated results.

Home Square Footage (sq ft): 1,000; Climate Zone: Mild (e.g., Southern California); Insulation Quality: Average

Estimated BTU Requirement: 30,000 BTU/hr; Recommended Furnace Size: 30,000 BTU/hr

Home Square Footage (sq ft): 1,500; Climate Zone: Moderate (e.g., Central US); Insulation Quality: Average

Estimated BTU Requirement: 52,500 BTU/hr; Recommended Furnace Size: 53,000 BTU/hr

Home Square Footage (sq ft): 2,500; Climate Zone: Cold (e.g., Northern US); Insulation Quality: Good

Estimated BTU Requirement: 80,000 BTU/hr; Recommended Furnace Size: 80,000 BTU/hr

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