KEVOS® MAKEOS · Materials
Hot Surface Insulation Check (Bare Loss, Insulated Loss, Touch Temperature, Payback)
How much heat does this hot surface lose bare and with insulation, is the insulated surface safe to touch, and how quickly does the insulation pay for itself?
Check of insulation for a hot flat surface (tank wall, oven casing, duct): bare-surface loss by radiation (as the radiant heat loss tool) plus convection, insulated loss through the insulation and the outer surface film (as the layered wall heat flow tool), the outer surface temperature against your touch limit, the yearly energy saving and the payback of the insulation cost.
Open the calculatorRuns in your browser. No account needed.
How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Surface area | m² | Area of the hot surface. |
| Hot surface temperature | °C | Temperature of the hot surface (the metal under any insulation). |
| Surroundings temperature | °C | Temperature of the surrounding air and surfaces. |
| Emissivity of the bare surface | Emissivity of the bare surface. | |
| Convection coefficient of the bare surface | W/(m²·K) | Natural or forced convection coefficient of the bare surface. |
| Insulation | ||
| Insulation thickness | mm | Thickness of the insulation. |
| Insulation conductivity | W/(m·K) | Thermal conductivity of the insulation at its mean temperature. |
| Outer surface film coefficient (convection + radiation) | W/(m²·K) | Combined convection and radiation film coefficient of the insulated outer surface (cladding). |
| Costs and limits | ||
| Hours hot per year | h | Hours per year the surface is hot. |
| Heat energy price | $/kWh | Cost of a kilowatt-hour of heat delivered. |
| Insulation cost per square metre | $/m² | Installed cost of the insulation and cladding per square metre. |
| Largest outer surface temperature | °C | Highest outer surface temperature allowed for people. |
| Longest payback accepted | years | Longest payback you accept. |
Method and formulas
- Radiation = ε σ A (T_s⁴ − T_a⁴) (as the radiant heat loss tool); convection = h_c A (T_s − T_a).
- Insulated: U = 1 ÷ (t ÷ k + 1 ÷ h_out); loss = U A ΔT; outer surface = T_a + U ΔT ÷ h_out (as the layered wall heat flow tool).
- Saving = (bare − insulated) × hours × price; payback = insulation cost ÷ saving.
- Example: bare it loses 33.151 kW, insulated 1.2963 kW; the outer surface runs at 37.963 °C and the insulation pays back in 0.4709 months.
Limitations
- Flat surface; pipes need the cylindrical form.
- Film coefficients as entered; wind raises the bare loss considerably.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Justify insulating a tank, oven or duct
- Choose an insulation thickness for personnel protection
- Estimate energy saved by lagging
Who it is for
- Energy managers
- Maintenance engineers
- Plant engineers
What you get
- Bare loss by radiation and convection
- Insulated loss and outer surface temperature
- Saving and payback
Interpreting the result
- The first few millimetres of insulation save the most: extra thickness is often set by the touch temperature rather than by energy.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 371–378. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
