Nice take on the tower defense genre. I like the idea of using a coal burner to melt down ice to make room for more towers.
The clean and easy to read art style is also nice although the level is rather empty, some objects would be nice, maybe frozen trees or frozen rocks, in general stuff that makes the melting and finding new spots more interesting. The hex grid is also a nice addition and not often seen in tower defense games.
It could be a really nice game if you would flesh it out a bit more and maybe add a bit more depth to it, maybe buildings to produce more resources or different types of towers.
Good job!