Why do Zamboni machines use hot water?

Answer 1

The Zamboni machine uses a large auger with sharpened edges to scrape the ice, removing gross imperfections. Brushes then direct the ice shavings and any chips, up a chute to a reservoir where it is mixed with hot water (in order to melt the shavings). The hot reservoir water is directed back down to the ice, behind the auger, in a very thin sheet that immediately freezes over the very cold surface of the ice, leaving an almost perfectly smooth, frozen surface behind.

Use of hot water, reason #1:

Hot water efficiently melts the ice shavings that they pick up while scraping the rough surface of the ice so that it can be recycled. If cold water were used, the Zamboni water-reservoir would get bound up with chunky ice-water. Returning this slushy material to the ice would cause a rough imperfect surface.

Use of hot water, reason #2:

The clarity of the ice surface is as important as the consistency. Imperfections in the new surface will cause some opacity, detracting from the clarity of the new ice. This problem is minimized by the use of hot water, which liquifies most potential imperfections.

Use of hot water, reason #3:

If the water came out cold, the roughened surface left by the auger, might not fully melt to be incorporated into a solid clear ice surface. Also, any shavings or chips, left on the ice, might not be melted, and would form imperfections in the ice surface.

These machines rely on the relatively large surface area of the shaved ice and on the rate of heat transfer in water, to melt the shaved ice in preparation for resurfacing.

Warm water can (under certain rare circumstances) freeze faster than cold water. But Zamboni machines do not rely on this phenomenon.

You can observe the areas where the Zamboni cannot reach (along the edges of the curved areas), and see how the areas covered by the Zamboni differ from these relatively untreated areas.