Heat-Loss Calculator › Brewery › Reference › DN65 (2½″) @ 120°C
Heat loss from a DN65 (2½″) pipe at 120 °C
A bare DN65 (2½″) pipe running at 120 °C in 20 °C still air loses about 239 W per metre. Wrap it in 50 mm of removable lamella mat and loss drops to about 36 W/m — a 85% cut — while the outer surface falls to about 27 °C (touch-safe). Figures use the ASTM C680 steady-state method.
These conditions are typical of low-temperature hot-water (LTHW) heating loops, condensate-return lines and hot process water. The temperature is modest, but the line runs continuously, so a bare run quietly wastes fuel all year — and the surface can still sit above the touch-safe limit.
Per-metre heat loss
| Quantity | Bare | Insulated (50 mm) |
|---|---|---|
| Heat loss | 239 W/m | 36 W/m |
| Heat loss (imperial) | 248.7 BTU/hr·ft | 37.7 BTU/hr·ft |
| Reduction | — | 85% |
| Outer surface temp | ~120°C | 27°C |
| Conductivity k (at 70°C mean) | — | 0.052 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 DN65 (2½″) line at 120 °C, with different removable-insulation thicknesses (lamella mat, k≈0.052 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 | 55 W/m | 77% | 34°C |
| 40 mm | 41 W/m | 83% | 28°C |
| 50 mm | 36 W/m | 85% | 27°C |
| 75 mm | 29 W/m | 88% | 24°C |
| 100 mm | 25 W/m | 90% | 23°C |
Because the process temperature is moderate, modest insulation already brings the surface well into the touch-safe range while still cutting most of the loss.
Example: a 50 m line with 4 valves
| Result | Value |
|---|---|
| Heat loss, bare | 12.5 kW |
| Heat saved by insulation | 10.6 kW |
| Fuel energy saved | 100.0 MWh/yr |
| Money saved | €7,002/yr |
| CO₂ avoided | 20.0 t/yr (≈ 4.3 cars off the road, 953 trees, 4.2 homes’ power, 46 barrels of oil, 81,923 km of driving or 20 transatlantic flights) |
| Payback (removable insulation) | 1.0 years |
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 quoteDoes a DN65 (2½″) line at 120 °C really need insulating?
Yes — a bare DN65 (2½″) line at 120 °C loses about 239 W per metre continuously, and over 8000 h/yr that is real, recoverable fuel. Removable insulation also keeps the surface touch-safe for personnel.
Related heat-loss tables
DN65 @ 150°CDN65 @ 180°CDN65 @ 200°CDN65 @ 250°CDN65 @ 300°CDN65 @ 350°CDN25 @ 120°CDN40 @ 120°CDN50 @ 120°CDN80 @ 120°CDN100 @ 120°CDN125 @ 120°CDN150 @ 120°CDN200 @ 120°CAll tables →Cutting these losses in practice: removable Inzonex Modular Insulation for valves, flanges and steam lines.