Burner BTU & Heat-Up Time Calculator
Heat-up time for your propane burner, the BTU/kW needed to hit it, and how much propane a boil burns.
Times assume steady output and the efficiency you set - wind, a bare flame or a lid change it a lot. Volume, temps and boil time carry across your other equipment tools.
How it works
Heating water takes a fixed amount of energy - 4.186 kJ per litre per °C. Divide that by the power your burner actually delivers (its rating times efficiency) to get the time. Propane burned is separate: it depends only on the burner rating and run time, since the fuel is consumed whether the heat reaches the pot or not.
energy (kJ) = litres × 4.186 × (target − start)°C
heat-up time = energy ÷ (burner kW × efficiency)
propane (lb) = burner BTU/hr × hours ÷ 21,594
Efficiency is the soft number here - measure a real heat-up once and back it out to calibrate your own setup. For an electric build, use the element calculator.
Sources: standard thermodynamics (specific heat of water); 1 BTU = 1.05506 kJ; propane higher heating value ≈ 21,594 BTU/lb.
Frequently asked questions
- How many BTU do I need to boil?
- It depends on volume, how cold you start and how much of the flame's heat actually reaches the pot. A typical outdoor propane banjo burner is 30-50% efficient - a lot of heat blows past the kettle. This tool takes your burner's rated BTU/hr and an efficiency figure and tells you the real heat-up time; drop the efficiency if you brew in wind or without a windscreen.
- Why is my real heat-up slower than the raw physics?
- The raw energy to heat water is fixed, but a burner never delivers all of it - the rest heats the air around the kettle. That is what the efficiency figure captures. At 40% efficiency a 60,000 BTU/hr burner only puts about 24,000 BTU/hr into the wort, so budget accordingly.
- How much propane does a brew day use?
- Propane burned depends only on the burner's rating and how long it runs (heat-up plus the boil), not on efficiency - the fuel is consumed whether or not the heat lands in the pot. Propane holds about 21,594 BTU per pound, so a 60,000 BTU/hr burner running an hour burns roughly 2.8 lb.