Critical Insulation Radius Calculator
Enter your own SI values to calculate using the stated idealized model. Calculations use only your local inputs. No material properties are looked up. This educational idealized model does not guarantee engineering sizing or safety.
A QUICK WALKTHROUGH
How to use this tool
- Enter the listed SI inputs; all material properties and geometry come from your inputs.
- Select Calculate and review the model assumptions and the results.
- Copy the report or download it as plain text. Changing an input clears the previous result.
Formula and SI units
Cylinder: rc = k/h; sphere: rc = 2k/h. Inputs use the units shown beside each field. Temperatures, where present, are absolute kelvin.
Assumptions and limits
Steady radial conduction through homogeneous insulation with constant conductivity and uniform external convection. The cylinder is long enough to neglect end effects; the sphere is concentric. Radiation, contact resistance, and changing convection coefficients are excluded. The critical radius is a stationary maximum heat-loss point in this ideal model when it lies in the physical radius range; it is not a recommended insulation thickness.
Local processing
Calculations use only your local inputs. No material properties are looked up. This educational idealized model does not guarantee engineering sizing or safety.
Official course references
MIT OpenCourseWare, Introduction to Heat Transfer equation sheet: https://ocw.mit.edu/courses/2-051-introduction-to-heat-transfer-fall-2015/e32f70f7e00f34953447b606cea0421f_MIT2_051F15_EqnSheet_Q2_v3.pdf ; Thermal Energy, heat-transfer notes: https://ocw.mit.edu/courses/16-050-thermal-energy-fall-2002/87d9f4544b7fd64a77201382500d057c_10_part3.pdf
GOOD TO KNOW
Common questions
Are material properties supplied automatically?
No. Choose values appropriate to your material and conditions from your own source.
Does this establish a safe engineering design?
No. It is an idealized educational calculation and does not verify the material, boundary conditions, or design.
Are inputs uploaded or saved?
No. The calculation and optional plain-text report are generated in your browser. The tool does not upload or persist the inputs.