Plus, the air in the oven isn't going to do much versus the thermal mass of your entire mash. Just think of it as being super-effective insulation.Caught one hell of a cold right after posting this. My oven only gets down to 170. Won't a oven set at 170 raise a 150 degree mash? It must only raise the temp slightly over an hour?Preheat to 170F. Turn it off before you start the mash, it takes some time to mix and adjust the temp if you are a little off. It takes some time to measure and adjust pH if you are one of those pH guys like me. Then when you are done, put it in the oven, which will be less than 170F. You could have an oven thermometer in there to tell you when the temp is 150F or a 150F +.