Heat-Loss Calculator › Reference › DN25 (1″) @ 300°C
Heat loss from a DN25 (1″) pipe at 300 °C
A bare DN25 (1″) pipe running at 300 °C in 20 °C still air loses about 294 W per metre. Wrap it in 50 mm of removable wired mat 80 and loss drops to about 68 W/m — a 77% cut — while the outer surface falls to about 36 °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 | 294 W/m | 68 W/m |
| Heat loss (imperial) | 305.6 BTU/hr·ft | 70.7 BTU/hr·ft |
| Reduction | — | 77% |
| Outer surface temp | ~300°C | 36°C |
| Conductivity k (at 160°C mean) | — | 0.057 W/m·K |
How much insulation thickness?
The same DN25 (1″) line at 300 °C, with different removable-insulation thicknesses (wired mat 80, k≈0.057 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 | 95 W/m | 68% | 56°C |
| 40 mm | 76 W/m | 74% | 41°C |
| 50 mm | 68 W/m | 77% | 36°C |
| 75 mm | 57 W/m | 81% | 30°C |
| 100 mm | 50 W/m | 83% | 27°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 | 15.4 kW |
| Heat saved by insulation | 11.8 kW |
| Fuel energy saved | 111.4 MWh/yr |
| Money saved | €7,796/yr |
| CO₂ avoided | 22.3 t/yr (≈ 4.8 cars off the road, 1,061 trees, 4.6 homes’ power, 52 barrels of oil, 91,212 km of driving or 22 transatlantic flights) |
| Payback (removable insulation) | 8.5 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 300 °C, and is it dangerous?
The bare metal sits near the process temperature on a DN25 (1″) line at 300 °C — far above the ~60 °C burn threshold and a serious safety risk. It also loses about 294 W/m, so insulation cuts the loss and returns the surface to safe-to-touch.