Originally Posted by WilliamWS
Not saying that method didn't work for you but a couple of concerns with that method:
First, I would think that, in doing a small mini-mash as has been proposed, putting around a gallon of water and 2.5 lb of grain in a 170F oven would would run a good chance of heating the works up to 170 (thus denaturing the enzymes) before conversion is complete.
Also, ovens are notoriously inaccurate. Their temperature can be off by 10-20 degrees (up or down) if you set it at 170 and it's actually 150 or 160 then great. But if it's really 180 or 190, no-so-great.
It's really not much of an issue if your mini-mash drops below your target temp for a bit-just heat it back to temp. But if it gets too hot and the enzymes are killed there's no going back.
Stir and check the temp every 15-20 minutes and no worries. The oven never heated the mash more than a couple degrees over an hour. I used more than a gallon of water though, it was more like 2.5-3.5 gallons.
I am not using the oven to hit my mash tun I am using it as an insulator to maintain the temp for an hour. For that purpose accuracy is not required, if anything just stick a probe thermometer in the mash and keep an eye on it. Too hot --> take it out of the oven for a couple minutes
Heating any significant volume of water in an oven is extremely inefficient, especially with a 10 or 20 or 40 degree temp difference between the mash and the oven temp. If you were mashing for 12 hours you may end up getting the mash up to the oven temp. But in an hour you don't have to worry. Worst comes to worst just turn the oven off or open the door a bit.