A device similar to the hot box described is available commercially from
Better Way Wax Melters
116-11th St. S.E.
Altoona, Iowa 50009
(515) 967-4952
They have sizes for 15 frames and up.
I used it to melt a large number of brood frames I received from a beeekeeper.
It worked fine. The frames could be scraped clean and reused. However I felt
that new frames were worth the expense.
It also does a good job of melting cappings and queen excluders.
Good Luck