While writing the recent piece on home heating, I was surprised to calculate many different numbers for the energy return on firewood. Though the outputs were only slightly different in quantity of BTUs, there was a wide range of inputs. But the primary reason for the return disparity was the presence of the market economy - those processing firewood for their own use had higher energy returns than those selling wood for profit - the accelerated drying time to process large amounts of wood required an additional wood input which dropped the energy return. Graphically this showed up as a tradeoff between maximizing energy return on TIME versus maximizing energy return on ENERGY. This reminded me that energy return is not a hard-and-fast principle, and also that society, obviously, will optimize its resources based on what it perceives to be its most limiting input(s). However, in an upcoming world constrained by energy, or any limiting variable other than time/money, we can increase our energy available by reducing the return on other inputs, such as time.