Thanks Robin and Timothy!
Lawrence, you are right on. Definitely be conservative with supplemental heat. A good insulated box goes a long way. There are also other things you can do like cover half of the heat pack with packing tape to keep it a little cooler, or put extra holes in the box if you like to do that (I do). You also don't want the animal right on top of the heat pack. Your goal with a heat or cool pack is to raise or lower the ambient temperature, not provide a hot spot or cold spot for the animal to sit on.
Reply With Quote