Factual error: According to netstate.com the average monthly high in the state of Louisiana is 93.3 degrees F (34.05 degrees C) with summer months often exceeding 100 degrees F (37.77 degrees C), making it impossible for a functional multi-story wax structure to remain functional for any extended period of time, regardless of wax content.
Factual error: Wax doesn't burn, even when exposed to flame. Wax also will not conduct heat. The ending shows the House of Wax melting and burning to the ground, as if the heat is spread throughout the house. In actuality, only the small hole near the fire will melt; the rest of the house would be unharmed.
Answer: It is simply a contraption to keep Wade in place so he doesn't move and the wax can be applied. It's also used to keep the wax out of his eyes, ears, nose and mouth.