Methodology guide
Limits, conversion, and when to stop shopping portable diesel heaters.
Calculator
Garage heater BTU calculator
Enter length, width, height, insulation level (1–5), and temperature rise. Get BTU/h, kW, cubic feet, and a diesel heater class or NO_MATCH.
Result
BTU/h = length × width × height × factor × ΔT. Factors: 1→0.093, 2→0.113, 3→0.133, 4→0.153, 5→0.173. Worked check: 20×22×8×0.133×40 = 18,726 BTU/h ≈ 5.49 kW → 8 kW class.
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