A rocket mass heater will burn cleanly no creosote to condense inside flue channels and heat a masonry or cob mass warming the water while absorbing some heat from the water during the day.
Thermal mass water storage tanks.
It is kept liquid at 288 c 550 f in an insulated cold storage tank.
With proper insulation of the tank the thermal energy can be usefully stored for up to a week.
Water contained in low cost non pressurized cylinders has proven to be the most practical and effective approach to the capture and storage of thermal energy for space and hot water heating.
Warm and chilled water enters and exits the tank through diffusers located at the top and bottom of the tank.
As rock or masonry.
The liquid salt is pumped through panels in a solar collector where the focused sun heats it to 566 c 1 051 f.
In other words it is the ability of a body to store thermal energy.
What is water storage tank and thermal mass.
Water stores 3 to 4 times as many btu s per lb.
It is then sent to a hot storage tank.
I think you would find it effective and easier to have separate thermal mass in contact with the water tanks and heated by the fire.
If you check the specific thermal capacity value for various materials you will notice that water has a remarkably high thermal mass.
It also releases this heat energy faster when you really need it.
No water coils or piping logistics needed.
We have tanks from 120 gallons up to 5 000 gallons for large solar heating systems of wood boiler system.