Multi-source heating design

Here's my concept for a heating design I'd like to try out.

Presently I have the standard gas/hydronic floor system and the concrete patio outside.

The next step would be the "rocket thing", and that's what I'm kind of fishing for input on.
(But comments on whatever are welcome)

I know they're usually made inside and all, but at this point I'd rather sacrifice a little efficiency and convenience to preserve the resale-ability of the house.
Therefore I was thinking of making something outside that I could simply disconnect and haul away when the time comes to move.

Yep that will work, you will just need a temperature regulating valve to knock down the higher temps of the rocket mass heater. You may, or may not, have one because of your existing solar set up. If you do, then you are all set. If not, you will need one as your concrete floor cannot have too high of a temp or it will cause your concrete to crumble.

You can get the desired knock down in two ways, a valve that I forget the name of, but it injects cold water into the system to knock down the high heat of the rocket mass heater. I am not a huge fan of these as it seems silly to use energy to create heat, only to snuff that heat out with blasts of cold water.

I like the metering valve, which is a computer controlled circulating pump that controls how much hot water from the main loop goes into the floor. Hooked to a PLC it checks the temperature outside, the water coming back from the in floor loop returns, the temperature of the slab, the main loop water temperature and calculates what the precise temperature should be. After installing one of these your thermostats and zone control valves will be basically useless because all the thermostats will do is tell your system whether it should be on or not. Because it checks these temperatures every minute, it will regulate how warm your house is, not by the thermostats shutting the zone valves on and off, but rather by how warm the water is flowing through your floor.

Oh...one more thing, you might want to consider putting in a back up generator. If the power goes out, and your rocket mass heater is fired up, the water failing to move by dead circulators will flash to steam, and then your own safety device is the 12 PSI relief valve in the system. Not a big deal, but there is also a second factor.

You could fill your system with Glycol so you do not freeze the system if you lose power. You will not freeze the system however as long as you do have power because the solar/gas back up unit will come on and keep the water at operating temperature, even if the rocket mass heater is outside. That however would freeze if you lose grid power without a back up generator. After calculating the cost of adding Glycol, and the 10% efficiency you will lose by using it, a back up generator is just as cheap to buy.