Sizes an electric trace-heating circuit for a pipe: computes the steady-state heat loss through the pipe's insulation at the design minimum ambient temperature, checks whether a selected heating cable's rated output (W/m) covers that loss with a safety margin, and checks the resulting circuit's current and voltage drop against the supply and breaker.
Standards followed
Standard cylindrical-conduction heat-loss formula (textbook heat transfer), applied per IEEE 515 electric resistance trace-heating practiceIEC 60079-30 for hazardous-area trace heating (GFEP requirement)
What it can do
- Steady-state heat loss (W/m) through the pipe insulation from pipe diameter, insulation thickness/conductivity, maintain temperature and design minimum ambient.
- Required heater output with a user-set design safety factor, checked against the selected heating cable's rated W/m.
- Circuit power and current from heater output and circuit length, checked against the breaker rating.
- Optional voltage-drop check for constant-wattage cable types with a known resistance per unit length.
Example problem
114mm OD pipe, 50mm mineral wool insulation (k=0.04 W/m·K), maintain 10°C at a -10°C design minimum ambient, 1.3 design factor, 20W/m heating cable, 80m circuit at 230V on a 16A breaker.
- ΔT = 10 − (−10) = 20°C.
- Heat loss = 2π × 0.04 × 20 / ln(0.214/0.114) = 7.98 W/m.
- Required with design factor = 7.98 × 1.3 = 10.38 W/m — the 20W/m cable comfortably covers this.
- Circuit power = 20 × 80 = 1,600W; current = 1,600/230 = 6.96A — well within the 16A breaker.
7.98W/m heat loss, 10.38W/m required, the selected 20W/m cable is adequate, and the 80m circuit draws 6.96A.
Want the full step-by-step version?
This sizes the heater and circuit from first-principles heat loss — it doesn't replace a manufacturer's heat-tracing design software, which accounts for pipe supports, valves/flanges, startup heat-up time, and cable de-rating for the specific installation. For constant-wattage cable types, enter the cable's resistance per meter to see the voltage-drop check; self-regulating cables have a non-linear resistance and aren't modeled here — check the manufacturer's maximum circuit length tables instead. Hazardous-area installations require GFEP (typically 30mA) per IEC 60079-30 — not modeled here as a pass/fail, just a reminder.