Originally Posted by Chad
You can do that by adjusting the heat on the stove up and down or you can bring your mash to temperature and put the covered pot into a preheated oven on the "warm" setting. Check the temp every 15 to 20 minutes to make sure you are within range.
It is 1,000x easier to hit your mash temp and throw the pot in a warm oven. Don't bother checking the temp, unless your stove is so poorly built that it can't hold a temp to bake, don't waste your time opening every 15 mins. I did the first few mashes, and I never needed to.
Set the oven to the lowest temp, usually ~175 or so, when it hits that shut if off. You can open the oven and place the mash in, opening the door will drop ~15-20 degrees. That coupled with the thermal mass of a gallon+ of water and all that grain is sufficient to maintain the temp.