inside the Peltier are a bunch of tiny peltier junctions in series. if you have it sideways, the units at the top are working in a hotter environment than the ones on the bottom which screws up the efficiency... having the cold on the bottom and hot on the top makes use those hundreds of little junctions are moving heat the same way.
![fellow fellow - พรุ่งนี้ไม่มีใครรู้ feat. INK WARUNTORN [OFFICIAL MV]](http://i.ytimg.com/vi/QP6JyjYx_W0/mqdefault.jpg)
Ah, found it. Why is it more efficient running hoeizontal?
inside the Peltier are a bunch of tiny peltier junctions in series. if you have it sideways, the units at the top are working in a hotter environment than the ones on the bottom which screws up the efficiency... having the cold on the bottom and hot on the top makes use those hundreds of little junctions are moving heat the same way.