I'm trying to calculate insulation thickness for a foundry, and can't figure it out after spending a few hours searching. Refractory: Kast-O-Lite Material Required: 1.44g/cm^3 Thermal Conductivity: 0.65 W/m*C Maximum inside temperature is 1648*C I figured there would be a minimum of 10,440 BTU/3057 Watts Required to melt 4.16L of Aluminum Inside Dimensions "Empty Space" would be 16cm Diameter x 23cm Tall Outside Dimensions: 31cm Diameter x 44.5cm Tall The closest thing I found to this would be Insulation thickness calculation for a pipe - EngCyclopedia However, I cannot figure out how to determine r2 Q=2*pi*k*N*((T1-T2)/ln(r2/r1) T1=50*C T2=1648*C r1=0.1524m r2=?? k=0.65 (W/m*C) N=0.2032m Q=2*pi*0.65*0.2032 Q=0.829883115*(-5198)/(ln(r2/0.1524) Can anyone help me out, or point me in the right direction? They say "Rule of Thumb" is 4inches/10cm of refractory. If I could just figure out what the outside temperature of that would be I think it would be helpful. Thank you very much!