On a working Cochran package boiler the rear back plate and the economizer behind it run at 126–130 °C — FLIR-measured, bare. Together they are the single largest uninsulated heat loss in the boiler house.
FLIR-measured surface tempsCAD areas × 1.4 bolt/irregularityISO 12241 · v = 0.5 m/s
This view. Visible in this angle: back plate (130 °C), economizer (126 °C), behind it — both bare.3D model: Inzonex · equipment rights belong to the manufacturer
Peak surface
130 °C
Bare, FLIR-measured
Largest loss
18.3 kW
Economizer
This view, bare
27.4 kW
2 element group(s)
After insulation
≈95%
Surface drops to ≤45 °C
Figures are for one boiler. Surface temperatures from a real FLIR survey of a UK commercial boiler house; CAD surface areas uplifted ×1.4 for bolts and irregular geometry; ISO 12241 steady-state (50 mm core, ambient 28 °C, air movement 0.5 m/s).
What you are looking at
How hot is a Cochran boiler back plate
The rear (back) plate of a Cochran shell boiler closes the reversal chamber, so the full flue-gas temperature presses against it — 130 °C across a 5.3 m² face. Bolted directly behind it sits the economizer, an 11.3 m² finned block at 126 °C that recovers flue heat but is almost always left completely bare because its shape resists rigid cladding.
These surfaces are the largest avoidable loss in the room. Running 8,000+ hours a year, the back of one boiler radiates tens of kilowatts continuously into the boiler-house air.
Element (this view)
Temp °C
Area m²
Bare W
Insulated W
Surface °C
Cut
Rear (back) plate
130
5.32
9,063
471
35
−95%
Economizer
126
11.31
18,327
954
34
−95%
Rear / back-plate view view, per boiler
16.6
27,390
1,425
≤45
−95%
ISO 12241, 50 mm Inzonex modular core, ε(bare)=0.9, ε(jacket)=0.85, hconv at 0.5 m/s. Insulated figures are conservative steady-state, not best-case.
Element by element
Why each one is left bare — and how it gets insulated
Rear (back) plate · 130 °C · 9.1 kW bare
A large, mostly flat face carrying the reversal-chamber heat. Easy to insulate, high payback — but usually left bare because it is “just the back”. A removable panel drops it from 130 °C to ≈35 °C and removes a burn hazard behind the boiler.
Economizer · 126 °C · 18.3 kW bare
The biggest prize and the most-skipped surface. Finned tube blocks and access doors make rigid lagging impractical, so economizers run uninsulated for their whole life. An Inzonex panel is shaped to the casing and re-opens for tube access, keeping recovered heat in the gas path.
Geometry that re-opens for access is the core idea behind the Inzonex modular design (UK patent application GB2508992.1).
