Expansion Joint Insulation: Heat Loss & Savings
Fabric and metal expansion joints on ducts, HRSGs and hot piping are almost always left bare — they move with thermal expansion, so fixed cladding cannot follow them. That makes them one of the single biggest avoidable heat losses on power and process plants. Removable insulation is purpose-made to flex with the joint.
Heat loss vs insulated — by surface temperature
| Surface temp | Bare loss | Insulated | Outer surface | Reduction |
|---|---|---|---|---|
| 190 °C | 3,696 W/m² | 194 W/m² | 33 °C | 94.7% |
| 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 fabric expansion joint (1.6 m², 280 °C) | 11.1 kW | 104 MWh | 21.1 t | €6,055 |
| A large duct expansion joint (3.0 m², 250 °C) | 17.0 kW | 160 MWh | 32.3 t | €9,282 |
FAQ
How much heat does a bare expansion joint lose?
At 20 °C ambient (ASTM C680): a fabric expansion joint (~1.6 m², 280 °C) loses about 11.1 kW; a large duct expansion joint (~3.0 m², 250 °C) about 17.0 kW. Insulating a fabric expansion joint saves ≈104 MWh and ≈21.1 t CO₂ per year (8,000 h).
Can you insulate round and rectangular fabric expansion joints and similar?
Yes. Expansion joints move and must be inspected for fatigue, so rigid insulation cannot be used. Inzonex removable joint covers flex with the bellows, unzip for inspection and refit with no damage. Inzonex covers round and rectangular fabric expansion joints, metal bellows and duct joints. The outer surface drops to a touch-safe ≤45 °C and the part stays serviceable.
How much does expansion joint insulation save?
Each item saves 96–98% of its bare loss. A fabric expansion joint at 280 °C saves ≈6,055 €/yr of energy (≈104 MWh, ≈21.1 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.