From this site's computed tables: insulating 46 bare valves and flanges (≈25 kW of standing loss) on a gas-fired steam system saves ≈244 MWh of fuel and ≈45 t CO2e per year at 8,000 h and 82% boiler efficiency — DESNZ 2024 factors. That single line is a complete SECR/E1-3 entry, and the Carbon Savings Certificate tool reproduces it for any kW figure.
From our guide: Scope 1 Reduction — full context, charts and sources there.