Heat transfer speed is in powder.h, in the ptypes array (the one with: {"DUST", PIXPACK(0xFFE0A0), 0.7f, 0.02f * CFDS, 0.96f, 0.80f,....)
Ins: specific heat value (how fast it transfers heat to particles touching it), can be found by using the real life heat value in J/G K (or KJ/KG K) by 96.635/RealLifeValue. 0 - no heat transfer, 250 - maximum heat transfer speed.