Furnace BTU Sizing Calculator

Size furnace BTU output for home heating loads.

Enter your project dimensions or values on the left. Results update instantly with a material breakdown you can share via the copy-link button.

Enter your project measurements using the defaults as a starting point, then adjust to match your room, wall, or yard.

Ordering exact quantities without waste leads to mid-project shortages. Measuring only one wall when the project wraps corners also under-orders materials.

These calculators use standard formulas and typical waste factors. Structural loads, code requirements, and site conditions vary by region. Consult a licensed contractor or engineer for load-bearing work, electrical service upgrades, and septic design.