Heat-Loss Calculator › Brewery › Reference › DN125 (5″) @ 250°C
Heat loss from a DN125 (5″) pipe at 250 °C
A bare DN125 (5″) pipe running at 250 °C in 20 °C still air loses about 1009 W per metre. Wrap it in 50 mm of removable lamella mat and loss drops to about 168 W/m — a 83% cut — while the outer surface falls to about 42 °C (touch-safe). Figures use the ASTM C680 steady-state method.
These conditions are typical of medium-pressure saturated-steam distribution and thermal-fluid (hot-oil) headers. Heat loss climbs steeply with temperature in this band, so removable insulation pays back fastest on exactly these lines.
Per-metre heat loss
| Quantity | Bare | Insulated (50 mm) |
|---|---|---|
| Heat loss | 1009 W/m | 168 W/m |
| Heat loss (imperial) | 1050.1 BTU/hr·ft | 174.8 BTU/hr·ft |
| Reduction | — | 83% |
| Outer surface temp | ~250°C | 42°C |
| Conductivity k (at 135°C mean) | — | 0.069 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 DN125 (5″) line at 250 °C, with different removable-insulation thicknesses (lamella mat, k≈0.069 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 | 265 W/m | 74% | 64°C |
| 40 mm | 195 W/m | 81% | 48°C |
| 50 mm | 168 W/m | 83% | 42°C |
| 75 mm | 129 W/m | 87% | 34°C |
| 100 mm | 108 W/m | 89% | 30°C |
This is the band where insulation economics are strongest — the heat saved per metre is high and the payback shortest.
Example: a 50 m line with 4 valves
| Result | Value |
|---|---|
| Heat loss, bare | 52.9 kW |
| Heat saved by insulation | 44.1 kW |
| Fuel energy saved | 415.0 MWh/yr |
| Money saved | €29,048/yr |
| CO₂ avoided | 83.0 t/yr (≈ 18.0 cars off the road, 3,952 trees, 17.3 homes’ power, 192 barrels of oil, 339,866 km of driving or 83 transatlantic flights) |
| Payback (removable insulation) | 4.1 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 quoteWhy does insulating a DN125 (5″) line at 250 °C pay back so fast?
Because heat loss rises steeply with temperature: a bare DN125 (5″) line at 250 °C loses about 1009 W/m, so the money saved per metre is high. Removable insulation on these lines typically pays back in well under two years.
Related heat-loss tables
DN125 @ 120°CDN125 @ 150°CDN125 @ 180°CDN125 @ 200°CDN125 @ 300°CDN125 @ 350°CDN25 @ 250°CDN40 @ 250°CDN50 @ 250°CDN65 @ 250°CDN80 @ 250°CDN100 @ 250°CDN150 @ 250°CDN200 @ 250°CAll tables →Cutting these losses in practice: removable Inzonex Modular Insulation for valves, flanges and steam lines.