But why fudge around the problem? Converting heat into power efficiently is one of science's great unsolved problems.
Read the links that I provided you. This has been discussed to death.
In short, ASIC's are 99.9% efficient at converting electricity to heat. Additionally, ASICs are very inexpensive to make if the initial investment, tape out , and testing costs are amortized over mass produced consumer products instead of a few thousand miners.
If the economics don't continue to evolve in this direction to being greener we can change a few lines of code.