I have built a coiled temperature controlled mash tun as described in the BYO article, http://byo.com/stories/issue/item/2799-build-a-heated-mash-tun-projects. Today was the third time that I have used it and it held the temps perfectly with no direct fire heat. I did use direct fire for the mashout.
This method appealed to me because I have a brutus build with three Blichmann 10 gallon pots. I often overshot temps during the mash and I had to pay very close attention to the mash temps. The extra equipment I needed was an element, controller, two thermowells,a few connections, tubing, and a coil (I purchased a 50 ft chiller.)
Today I was able to hold my mash at 156 for the entire mash. This was done by holding the hlt at 1.5 degrees C over that 156 degree. My Controllers are Celsius with a chart taped to the side.
1. Controllers - Two STC 1000's. I found a great video on HBT that showed how to make them.
2. HLT - This was the biggest change. I installed a heating element and a thermowell in the side of the pot. The element almost spans the entire pot so the thermowell is below the element. They are at 90 degrees locations from each other. I use a piece of high temp tubing as a heat shield. I also installed a water return in the lid. The element was purchased from Homebrewstuff.com.
3. Mash Tun - The only changes is the addition of the coil (wort chiller), a thermowell in the lid, and a notch cut in the lid for that chiller. I used a carboy thermowell for the lid with two small keg o-rings to hold it in place.