Flange Insulation: Heat Loss & Savings
Pipe flanges are left bare so the bolts can be checked and broken for maintenance, but each hot flange pair leaks heat continuously and creates a burn hazard. Removable flange covers stop the loss while still allowing access.
Heat loss vs insulated — by surface temperature
| Surface temp | Bare loss | Insulated | Outer surface | Reduction |
|---|---|---|---|---|
| 150 °C | 2,564 W/m² | 138 W/m² | 29 °C | 94.6% |
| 250 °C | 5,822 W/m² | 154 W/m² | 30 °C | 97.4% |
| 350 °C | 10,860 W/m² | 259 W/m² | 37 °C | 97.6% |
| 430 °C | 16,665 W/m² | 360 W/m² | 44 °C | 97.8% |
Per-m² flat-surface flux, ASTM C680 / ISO 12241, 50 mm Lamella (≤220 °C) or 100 mm Wired mat (>220 °C), 20 °C ambient. Multiply by the bare area.
Worked examples (per year, 8,000 h, natural gas)
| Item | Heat saved | Energy/yr | CO₂/yr | € saved/yr |
|---|---|---|---|---|
| A dn100 flange pair (0.22 m², 350 °C) | 2.3 kW | 22 MWh | 4.4 t | €1,273 |
| A large flange assembly (0.7 m², 280 °C) | 4.9 kW | 46 MWh | 9.2 t | €2,649 |
FAQ
How much heat does a bare flange lose?
At 20 °C ambient (ASTM C680): a DN100 flange pair (~0.22 m², 350 °C) loses about 2.3 kW; a large flange assembly (~0.7 m², 280 °C) about 4.9 kW. Insulating a DN100 flange pair saves ≈22 MWh and ≈4.4 t CO₂ per year (8,000 h).
Can you insulate weld-neck and similar?
Yes. Flange bolts must be accessible for torque checks and gasket changes. Inzonex removable flange covers come off in seconds and refit without tools damage. Inzonex covers weld-neck, slip-on, blind and orifice flanges. The outer surface drops to a touch-safe ≤45 °C and the part stays serviceable.
How much does flange insulation save?
Each item saves 96–98% of its bare loss. A dn100 flange pair at 350 °C saves ≈1,273 €/yr of energy (≈22 MWh, ≈4.4 t CO₂) at typical gas prices; payback is usually under two years.
What insulation thickness is used?
Up to 220 °C surface: 50 mm mineral-wool (Lamella); above 220 °C: 100 mm (Wired mat), because conductivity rises with temperature. Both keep the outer surface ≤45 °C.