Q. What is Rabbi Miller’s position on doing chazara on Warming Drawers.

A. Our sages imposed a prohibition on placing or returning any food, even if fully cooked, directly on a blech or covered fire or other heat source on Shabbos unless certain conditions are met. The reason is that this constitutes “Michzei Kemevashel” or it looks like one is actually cooking in Shabbos. (Rashi – Shabbos 36b, Mishna Berura 253: 37.)
Horav Shlomo Millers Shlita opinion is that it depends if the warming drawer has its own source of heat or it just retains some of the heath of the oven on top of it. In the latter case it would be permitted. The Rov pointed to Mishna Berura (ibid. 14) where he quotes different opinions in regards to “smicha” or returning food which is only close to a heat source, and it seems that the Mishna Berura tends to the lenient opinions. He also (ibid.) quotes that some Poskim permit even on the onset, to place close to a heat source cooked food that is still warm. Especially in regards to the old kind of stove drawers, were the heat source is on top, as heath rises.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a