Heat-Loss Calculator › Brewery › Reference › DN40 (1½″) @ 350°C
Heat loss from a DN40 (1½″) pipe at 350 °C
A bare DN40 (1½″) pipe running at 350 °C in 20 °C still air loses about 501 W per metre. Wrap it in 50 mm of removable wired mat 80 and loss drops to about 106 W/m — a 79% cut — while the outer surface falls to about 43 °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 | 501 W/m | 106 W/m |
| Heat loss (imperial) | 520.9 BTU/hr·ft | 109.8 BTU/hr·ft |
| Reduction | — | 79% |
| Outer surface temp | ~350°C | 43°C |
| Conductivity k (at 185°C mean) | — | 0.061 W/m·K |
This chart shows the dramatic reduction in heat loss when insulation is applied. The orange bar represents the insulated condition with 50 mm of mineral wool.
How much insulation thickness?
The same DN40 (1½″) 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 | 152 W/m | 70% | 69°C |
| 40 mm | 119 W/m | 76% | 49°C |
| 50 mm | 106 W/m | 79% | 43°C |
| 75 mm | 86 W/m | 83% | 34°C |
| 100 mm | 75 W/m | 85% | 30°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 | 26.2 kW |
| Heat saved by insulation | 20.7 kW |
| Fuel energy saved | 194.9 MWh/yr |
| Money saved | €13,644/yr |
| CO₂ avoided | 39.0 t/yr (≈ 8.5 cars off the road, 1,856 trees, 8.1 homes’ power, 90 barrels of oil, 159,631 km of driving or 39 transatlantic flights) |
| Payback (removable insulation) | 5.4 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 DN40 (1½″) line at 350 °C, and is it dangerous?
The bare metal sits near the process temperature on a DN40 (1½″) line at 350 °C — far above the ~60 °C burn threshold and a serious safety risk. It also loses about 501 W/m, so insulation cuts the loss and returns the surface to safe-to-touch.
Related heat-loss tables
DN40 @ 120°CDN40 @ 150°CDN40 @ 180°CDN40 @ 200°CDN40 @ 250°CDN40 @ 300°CDN25 @ 350°CDN50 @ 350°CDN65 @ 350°CDN80 @ 350°CDN100 @ 350°CDN125 @ 350°CDN150 @ 350°CDN200 @ 350°CAll tables →Cutting these losses in practice: removable Inzonex Modular Insulation for valves, flanges and steam lines.