The temperature of hammerspace is around 294 degrees Kelvin. This temperature is maintained by the transdimensional fold or warp energy produced when objects are brought into or taken out of hammerspace. To put it another way, hammerspace exists in a multi-dimensional universe and the transitory collapse into a three (or a two) dimensional world releases vast amounts of energy some of which, according to the second law of thermodynamics, is manifested as heat.
Doesn’t everyone know that?