I built one last year,a keystone stove but I can't use it in this greenhouse. I may bury the milk can in the floor for now to store the heat from the cooling process longer. It is still cold enough here to need a second shelter in the greenhouse. To leave the plants out there overnight...This is a new to me solaraim still under construction. It will eventually be heated by hydronic solar. For now some thermal mass will get me through this spring. Cooling will be a problem very soon. I had temps from 31* Ina four foot deep pit to 132* say the ceiling vent at the same time yesterday. It is 21* n there this morning.