That's the problem with them and if you're trying to get as cold/warm as possible you have to consider this: The highest current I could draw with one of them at Starting (without thermal gradient) is 4.2A at 12V assuming a go to 5A. This varies from slab to slab and there is almost never the same force on any one of the slabs. The reason for this is that the temperature gradient isn't as high on either side of the plate when not drawing as much current, meaning you don't get really high or low