There is only one time that I use heat.
I will use the standard A/B tek with HCl and NaOH. I will never use either straight. I will dissolve the NaOH in distilled water, and allow it to cool. Even if it didn't create heat, undiluted NaOH will rip DMT apart like it will any organic molecule.
After I have done a few naphtha pulls, I will put my jars with basic solution and naphtha in a water bath and invert a few times as it heats up. I'll try to keep the solution around 50C for about 30 minutes, inverting every five minutes or so. This allows me to maximize DMTs solubility for the final pull. I will turn off the heat and pull the naphtha while it's still near 50C.
I have recently quit using HCL and NaOH. I now use vinegar and sodium carbonate. I find that the vinegar is just as effective as long as you aren't in a hurry and is MUCH safer. The sodium carbonate requires a bit more to get the pH up but can be added directly to solution thus requiring less volume and of course, safer.