Calculate the real heater power at your voltage, the current and the minimum fuse. The calculator also suggests a safe power for the chosen column diameter to avoid flooding.
How do I calculate heater power?
Heater power depends on the square of the voltage: P = U² / R. A drop in mains voltage from 230 V to 215 V therefore lowers power by about 13%. You can measure resistance with an ordinary multimeter on the disconnected heater.
Heating power vs. column diameter
A column has limited vapour capacity. When the power is too high, the vapour holds back the descending reflux and the column floods – you hear gurgling and the temperature jumps. A safe working power is usually 60–80% of the flooding power. A heater power controller lets you set it precisely.
Electrical safety
Above 16 A a standard socket and 2.5 mm² cable may not be sufficient. Connect high-power heaters to a separate circuit with proper protection, ideally via a residual current device (RCD).
How we calculate
Power P = U² / R, current I = U / R (or I = P / U). The flooding power of a spring-packed column grows with its cross-section – we assume about 1.2 W per mm²; working power is usually 60–80% of the flooding power. Values are approximate and depend on packing and insulation.
Frequently asked questions
How do I measure heater resistance?
Disconnect the heater from the mains and measure the resistance between its terminals with a multimeter. A 2000 W/230 V heater has about 26.5 Ω.
Why does my column flood?
With too much power the vapour cannot pass through the column cross-section and holds back the descending reflux. Reduce the power or use a power controller.
Can I combine two heaters?
Yes – their powers add up. Ideally connect them to separate circuits and switch one off after the wash has heated up, so the column does not flood.
Can a heater be switched on without water?
No. The heater must be fully submerged, otherwise it overheats and burns out within seconds. Always fill the boiler first and only then switch on the power.
What is a power controller for?
A controller lets you smoothly reduce heater power, e.g. from 3 kW to 1.5 kW. This way you can heat the wash quickly at full power and then run the column steadily at working power.
What heater power for a 50 l still?
For heating up a 50 l boiler 3–4.5 kW is convenient, while a 2" column usually runs on 1.2–1.8 kW. A strong heater with a power controller works best.