Sizes the trace-heating cable output for freeze protection: steady-state radial heat loss through the insulation plus a design safety margin, checked against your candidate cable rating.
Indicative only. Verify final design to project spec, IEEE 515.1 and IEC/IEEE 62395.
For design guidance only. Always verify with a qualified engineer.
About this freeze protection calculator
This free freeze protection and trace heating calculator sizes the electric heating-cable output needed to keep a pipe above freezing in cold weather. It works out the steady-state heat the pipe loses through its insulation and outer surface, adds a design safety margin, and compares the result against a candidate cable's nominal output to tell you whether it is adequate or insufficient. Enter the bare pipe outside diameter, the insulation thickness and conductivity, the maintain and minimum-ambient temperatures, the outer surface film coefficient, a safety margin, the cable's rated output and the traced run length. It returns the design ΔT, the conduction and surface-film resistances, the base heat loss per metre, the required cable output per metre, the spare capacity of your chosen cable and the total run demand in watts. It is aimed at UK building-services and electrical engineers specifying self-regulating or constant-wattage trace heating at tender or design stage. Everything is computed in your browser; nothing is uploaded.
How the required cable output is calculated
The method follows the heat-loss-based cable-sizing approach of IEEE 515.1 and IEC/IEEE 62395, with the heat loss taken from the steady-state cylindrical resistance network of BS EN ISO 12241. The design temperature difference is ΔT = Tmaintain − Tambient. Heat loss per metre is Qbase = ΔT ÷ (Rcond + Rsurf), where the insulation conduction resistance is Rcond = ln(r₂/r₁)/(2πk) and the outer surface film resistance is Rsurf = 1/(h·2πr₂), with r₁ the pipe radius and r₂ the radius over the insulation. The required cable output applies a design safety margin (the Chromalox heat-trace guides use a 10% baseline): Qrequired = Qbase × (1 + margin/100). A cable is adequate when its nominal output at the maintain temperature is at or above Qrequired. The pipe surface is conservatively assumed to sit at the maintain temperature, so pipe-wall and inner-film resistance are neglected; convection is modelled explicitly through the film coefficient.
Frequently asked questions
What maintain temperature should I use for freeze protection?
Freeze protection typically maintains a pipe at around 5 °C, comfortably above 0 °C to allow for control tolerance and local cold spots. Set the minimum ambient to the coldest design air temperature the pipe will see; for an exposed outdoor run in the UK that is often around −10 to −15 °C.
Why does the calculator add a safety margin?
Manufacturers' published cable outputs are based on idealised conditions. A margin (commonly 10%) covers tolerances, ageing, support losses and imperfect insulation. The required output is the base heat loss multiplied by one plus the margin, and your cable must meet or beat that figure.
What happens with a bare, uninsulated pipe?
With zero insulation the conduction resistance is zero, so the only resistance is the outer surface film. Heat loss is then very high, often many times that of an insulated pipe, and the required cable output rises accordingly. Insulating the pipe is almost always cheaper than heating an unlagged one.