I am working on designing a outdoor fire place with a knee wall surround as a wind break.
I would like to implement some type hydronic/radiant heat flooring system as I would be laying a concrete patio/base with architectural stone surface.
My thinking is some type of tank next to the chimney to absorb the heat from the fire place.
However I need to work out some kinks as I am not very skilled with this type of system. ie: controls/vavles
Would like to keep as much of this system mechanical (controls) as possible.

Some issues I have are :
1. Could I use a typical automotive type anti-freeze solution either straight or mixed ? My concern here is possible damage to the system & or concrete during winter or non-use.
2. What type of controls/valves would I need/could use.

3. How would I figure load calcs. for a system of this nature. ie: tubing weave and size of tubing.
I would also need to make sure I have tank/radiator large enough to handle the load requirements.

I will also be using dead spaces behind the actual firebrick/fire place to install a squirrel cage ventilation system as a supplemental heat, venting out the front of the fireplace if needed.

Any help or input in regards to any of these thoughts would be greatly appreciated.

It will probably be next spring/summer before actually starting this job as I am still working out some issues and its pretty cold here now but will post some pic after completion.