Heat-Loss Calculator › Brewery › Reference › DN100 (4″) @ 150°C
Heat loss from a DN100 (4″) pipe at 150 °C
A bare DN100 (4″) pipe running at 150 °C in 20 °C still air loses about 467 W per metre. Wrap it in 50 mm of removable lamella mat and loss drops to about 67 W/m — a 86% cut — while the outer surface falls to about 30 °C (touch-safe). Figures use the ASTM C680 steady-state method.
These conditions are typical of low-pressure saturated steam, medium-temperature hot water (MTHW) and thermal-oil return lines. A bare surface here is already a burn risk and loses a large, continuous amount of heat that insulation recovers almost entirely.
Per-metre heat loss
| Quantity | Bare | Insulated (50 mm) |
|---|---|---|
| Heat loss | 467 W/m | 67 W/m |
| Heat loss (imperial) | 485.6 BTU/hr·ft | 69.2 BTU/hr·ft |
| Reduction | — | 86% |
| Outer surface temp | ~150°C | 30°C |
| Conductivity k (at 85°C mean) | — | 0.055 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 DN100 (4″) line at 150 °C, with different removable-insulation thicknesses (lamella mat, k≈0.055 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 | 105 W/m | 77% | 40°C |
| 40 mm | 77 W/m | 84% | 33°C |
| 50 mm | 67 W/m | 86% | 30°C |
| 75 mm | 51 W/m | 89% | 26°C |
| 100 mm | 43 W/m | 91% | 24°C |
At this temperature the bare surface burns on contact within a second; 50 mm of removable insulation typically returns it to a touch-safe ≤45 °C.
Example: a 50 m line with 4 valves
| Result | Value |
|---|---|
| Heat loss, bare | 24.5 kW |
| Heat saved by insulation | 21.0 kW |
| Fuel energy saved | 197.4 MWh/yr |
| Money saved | €13,819/yr |
| CO₂ avoided | 39.5 t/yr (≈ 8.6 cars off the road, 1,880 trees, 8.2 homes’ power, 91 barrels of oil, 161,681 km of driving or 39 transatlantic flights) |
| Payback (removable insulation) | 7.7 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 quoteIs a bare DN100 (4″) line at 150 °C a burn hazard?
Yes — a bare DN100 (4″) surface at 150 °C exceeds the ~60 °C touch-safe threshold (ASTM C1055, EN ISO 13732-1) and burns on brief contact. The line also loses about 467 W/m, so insulation fixes safety and energy at once.
Related heat-loss tables
DN100 @ 120°CDN100 @ 180°CDN100 @ 200°CDN100 @ 250°CDN100 @ 300°CDN100 @ 350°CDN25 @ 150°CDN40 @ 150°CDN50 @ 150°CDN65 @ 150°CDN80 @ 150°CDN125 @ 150°CDN150 @ 150°CDN200 @ 150°CAll tables →Cutting these losses in practice: removable Inzonex Modular Insulation for valves, flanges and steam lines.