small mass heater for greenhouse

[steveh2112]

hi, i'd like to build a small mass heater for a small greenhouse 8x12. i'm in upstate NY and like to protect the greenhouse from frost. i'm planning to use 1" insulation panel walls on the north side and double pane glass panels (2nd hand) for the roof and south wall so i think i don't need a big heater.  i'd like it to hold temperature 12 hrs if possible

to save money and time i was thinking about buying the $39 rocket stove on amazon www.amazon.com/Cooking-Portable-Burning-Camping-backyard/dp/B0BZ4D72QF/ref=sr_1_2_sspa and then wrapping it in insulation and then building a stratification chamber out of brick and using garden dirt and rocks for the heated bench thing. 

any thoughts? any other ideas for a cheap small mass heater?

thanks
i

[martyn]

Hi Steve, you will need to build a more suitable heater made from refractory materials, if you want to heat a mass for 12 hours, it will be quite big!
The problem with small J tube designs is the required permanent feeding of the fire.

[steveh2112]

thanks, so bigger fire and more heat but for a shorter time with lots of mass then. makes sense, less work