cob oven water heater idea

One of my teenagers came up with an idea that sounded brilliant at first reflection. Double checking with this crowd to make sure it is the bomb and not A BOMB of the boom-squish variety.

His idea is to build you indoor and outdoor kitchen cob ovens back to back. The indoor oven would have a hood/double chamber and high-grade chimney to handle the heat. It would be your oven/hearth/heat stove for the house. Basically fire it up late afternoon early evening and it would be ready to bake first thing in the morning and give off wonderfull heat all night. Identical stove built outside for summer use. They share the backwall with each other.

What I thought was the really brilliant part: in the cob wall between them would be a water tank. Either stove would heat it year round, and the unused stove would act as insulation to keep the heat. The tank would be open to air (non pressurized) to prevent boom-squish and pumped on-demand. My addition was to install the tank inside above the oven and use a thermosiphon loop between the stoves instead and gravity fed to the rest of the house.

Brilliant or insane?

There is a distinct issue with it, largely that having a significant mass of water in your oven will limit it to around 212 degrees until it boils off.

Positioning it above the oven would probably help quite a bit, but if you're running tubes down into the oven, you get into issues with getting the water to siphon fast enough so that it doesn't flash off. I'd think that capturing waste heat from the chimney would be the way to go in a situation like this.

It wouldn't be directly in the stove, but in the mass/insulation layer that normally will be about 150 or so

Ahh, in that case I suspect it would work quite well.