Using water drums for solar heating?

If you are using metal water drums (like 55 or 30 gal. drums) for solar greenhouse heating, you should think about the addition of drum covers. Drums have a lip on top which can hold water and thus, the standing water in metal drums can promote premature rusting. A plastic lid prevents this rusting and lengthens the life of your water storage. To read more about energy conservation in the greenhouse click here.