Furnace Sizing Calculator
- Heat load BTU/hr
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- Furnace input size
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- Closest standard
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Output BTU = input × AFUE. Furnaces come in 40k / 60k / 80k / 100k / 120k input.
About this tool
Furnace Sizing Calculator is a single-purpose utility on instant.tw, a free toolbox of calculators, converters, generators, and quick lookups. Everything works in your browser — nothing is uploaded, nothing is stored on a server unless explicitly noted.
Category: Trade & Construction Calculators. Browse more Trade & Construction Calculators tools.