Heatsink

In order to get the best performance from a Peltier module, you need to be able to remove as much heat as possible from the hot side of the device. Several customers report that a PC water cooling setup is the best way to get dramatic heating and cooling results. If you're not using a water cooling setup, you need a substantial heatsink and fan to keep the module from reaching a warmish, useless equilibrium. No matter what you use, it needs to be very firmly attached with thermal grease/epoxy in the middle. Running the device without a heatsink on the hot side can permanently damage the module.

Reversing the polarity will switch which side is hot and which is cold, so you could, for example, heat & cool the inside of a box with one Peltier. A simple DPDT switch could be use for this, or if you prefer to do it electronically, a H-Bridge would work.

Heatsink Compound

Several customers report that a PC watercooling setup is the best way to get dramatic heating and cooling results with this thing. You need a substantial heatsink and fan to keep this thing from reaching a warmish, useless equilibrium, and some people seem to think that equilibrium is actually damaging to the Peltier. No matter what you use, it needs to be very firmly attached with thermal grease/epoxy in the middle. I tried just clamping our heatsink/fan to it and it didn’t work well enough.

Reversing the polarity (I bet an H-bridge would be nice for that…) will switch which side is hot and which is cold, so you could, for example, heat & cool the inside of a box with one Peltier.