Hi rabbi-I was wondering what you meant when you said that there is a rabbinic prohibition of generating heat-did the rabbi mean an issur of molid? Or is there a rabbinic prohibition of mav’ir? If it is the latter, what is the source for such an issur? Thanks so much chazak ubaruch

Indeed, in regard to hands warmers, Rabbi Lior Shlit"a in his book "Dvar Chevron" ,(siman. 236 pg. 125), refers to the Rabbinic issur of "molid" of creating heat and therefore only in special cases is it permitted.