Heat-Loss Calculator › Reference › DN25 (1″) @ 350°C
Heat loss from a DN25 (1″) pipe at 350 °C
A bare DN25 (1″) pipe running at 350 °C in 20 °C still air loses about 346 W per metre. Wrap it in 50 mm of removable wired mat 80 and loss drops to about 86 W/m — a 75% cut — while the outer surface falls to about 41 °C (touch-safe). Figures use the ASTM C680 steady-state method.
These conditions are typical of high-pressure or superheated steam headers and hot-oil supply lines. Bare metal at this temperature is a severe burn hazard and, near combustible residues or leaks, an ignition risk — so insulation is as much a safety as an energy measure.
Per-metre heat loss
| Quantity | Bare | Insulated (50 mm) |
|---|---|---|
| Heat loss | 346 W/m | 86 W/m |
| Heat loss (imperial) | 360.2 BTU/hr·ft | 89.5 BTU/hr·ft |
| Reduction | — | 75% |
| Outer surface temp | ~350°C | 41°C |
| Conductivity k (at 185°C mean) | — | 0.061 W/m·K |
How much insulation thickness?
The same DN25 (1″) line at 350 °C, with different removable-insulation thicknesses (wired mat 80, k≈0.061 W/m·K). Heat loss and surface temperature both fall as thickness increases — with diminishing returns past 50–75 mm.
| Thickness | Heat loss | Reduction | Surface temp |
|---|---|---|---|
| 25 mm | 120 W/m | 65% | 66°C |
| 40 mm | 96 W/m | 72% | 47°C |
| 50 mm | 86 W/m | 75% | 41°C |
| 75 mm | 72 W/m | 79% | 32°C |
| 100 mm | 64 W/m | 82% | 29°C |
Above 250 °C the calculator uses a wired mineral-wool mat (higher-temperature binder); confirm the hot-face material rating for superheated duty.
Example: a 50 m line with 4 valves
| Result | Value |
|---|---|
| Heat loss, bare | 18.1 kW |
| Heat saved by insulation | 13.6 kW |
| Fuel energy saved | 128.3 MWh/yr |
| Money saved | €8,983/yr |
| CO₂ avoided | 25.7 t/yr (≈ 5.6 cars off the road, 1,222 trees, 5.3 homes’ power, 59 barrels of oil, 105,096 km of driving or 26 transatlantic flights) |
| Payback (removable insulation) | 7.3 months |
Assumptions. 50 m pipe + 4 valves (each ≈0.6 m bare pipe), 8000 h/yr, 85% boiler efficiency, €0.07/kWh fuel, 0.20 kg CO₂/kWh, 50 mm insulation at €250/m². CO₂ equivalences use US EPA / DEFRA conversion factors. Change any of these in the live calculator. Estimates for guidance — confirm with a site survey.
Run your own numbers
Adjust size, temperature, thickness, hours and energy price live — or get an exact heat-loss study and fixed insulation price for your equipment list.
Open the calculator →Get an exact quoteHow hot is a bare DN25 (1″) line at 350 °C, and is it dangerous?
The bare metal sits near the process temperature on a DN25 (1″) line at 350 °C — far above the ~60 °C burn threshold and a serious safety risk. It also loses about 346 W/m, so insulation cuts the loss and returns the surface to safe-to-touch.