Electric Mashtun heating

I've been trying to figure out a good way of doing step mashes for a long time. Adding hot water works but is in my opinion troublesome. I brew with electricity and and indoors so i cant direct fire. Putting an element in my mash is also a no go obviously do to scorching. So im going to build a double boiler. Not a new or even complicated concept. Heat water in a chamber underneath the main vessel. Im going to have a valved inlet for refreshing the boiler water. And an outlet for keeping any pressure buildup regulated. Also a temperature probe to make sure things arnt goin crazy. If it works well im going to adapt the concept over to my boil kettle.

I'm no expert on these things, but you may want to consider a HERMS or RIMS system which should meet your requirements and they are probably easier to build. A double boiler should work, I'm just thinking most people that step mash either use HERMS or RIMS and that's probably done for a reason.

Most double boilers encapsulate at least the bottom half of the vessel. I think the bottom only idea would work as long as you recirculate the mash to distribute the heat applied at that focused spot. I don't think it would work on the boil kettle. You'd need to run steam to get it hot enough to boil the interior contents.