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.

Direct answer: a bare hot flange surface loses roughly 2,300 W/m² at 250 °C and 4,100 W/m² at 430 °C (20 °C ambient, ASTM C680). Inzonex removable insulation cuts that by about 91%; high-temperature cases use the appropriate build-up to meet the required touch-safe target.

Heat loss vs insulated — by surface temperature

Surface temp	Bare loss	Insulated	Outer surface	Reduction
150 °C	1,300 W/m²	134 W/m²	33 °C	89.7%
250 °C	2,300 W/m²	152 W/m²	35 °C	93.4%
350 °C	3,300 W/m²	255 W/m²	46 °C	92.3%
430 °C	4,100 W/m²	354 W/m²	55 °C	91.4%

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)	0.7 kW	6 MWh	1.3 t	€366
A large flange assembly (0.7 m², 280 °C)	1.7 kW	16 MWh	3.2 t	€925

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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 0.7 kW; a large flange assembly (~0.7 m², 280 °C) about 1.7 kW. Insulating a DN100 flange pair saves ≈6 MWh and ≈1.3 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 modular removable flange insulation comes off in seconds and refits without tool damage. Inzonex covers weld-neck, slip-on, blind and orifice flanges. The outer surface is reduced sharply; the insulation build-up is selected to meet the required touch-safe target while keeping the part serviceable.

How much does flange insulation save?

Each item saves up to 96% of its bare loss. A dn100 flange pair at 350 °C saves ≈366 €/yr of energy (≈6 MWh, ≈1.3 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. The build-up is selected by temperature: higher-temperature assets may need a thicker or higher-performance layer to meet a ≤45 °C touch-safe target.