abhege said: 
I got a barrel today so tomorrow I start digging!!! I'm excited to see if this can help heat my 16x12 greenhouse.
So, how air tight is your greenhouse, and what material is it made of? The better it is on these two factors, the better the barrel will work. Having the extra air holding volume in the barrel system makes a huge difference. If you only have one barrel to use holding air and water in the same drum will reduce the warm air volume which may lower the over all temperature. If i were to do this over, I might stack two barrels together and seal up where they join and bury those, so I could put more water in the barrel and have more below ground air space which would probably double it's effectiveness. Tom
