Available in different sizes, from as small as 35# per day, which is used in consumer applications, to over 1000# per day. Also, there are differences in the style of the ice itself, which may be in cubes, flakes, or shaved.
Ice makers are typically specified by the quantity of ice required. There are numerous sizes available, but in schools, the quantity usually specified is between 400# per day in small elementary schools, to 1000# or larger in comprehensive high schools that have several cold pans that need ice.
Besides output quantity, the biggest differences are the type of ice you want. A classic unit uses cubes. They may be of different sizes, from mini-cubes at .5″ square to around 1″ square. Some machines are flakers or shavers which are used a lot in restaurant bars, but not as much in schools. Other machines make a crescent shaped cube. However, the shape does not make a lot of difference. Some machines are all stainless steel and others use an epoxy coated galvalume finish. On commercial machines, the ice maker itself is modular, which means it mounts on top of an ice bin or an ice dispenser. If you are specifying more than one machine, such as one in the kitchen and two more, each on top of an ice/drink dispenser, you would probably size them each in the 400# size. There is a radical difference in production depending on the temperature of the incoming water and the ambient temperature where the machine is to be placed. A 400# machine in ambient of 70° with incoming water temperature at 50° will product up to 460# of ice. The same machine in 90° ambient with 70° incoming water will only product 360# of ice.
You need to know how much space is available. Also, the type and quantity of ice, where it is to be mounted, the size of the bin required, if necessary. Also, voltage available and proximity to a floor drain.
As with all water consuming products, it is imperative that the incoming water be treated to reduce the amount of minerals going into the machine. This can drastically affect the service required on the machine. Therefore, most ice maker manufacturers sell water treatment systems to work together with their machines. It is VERY important to specify this at the time you specify the equipment. It is important that you specify a bin that is big enough for your application. In a hospital, the ice is used over about 18 hours, where in a school the ice is consumed in about 4 hours. Therefore, the school has to have larger storage capacity than a hospital, even if they consume the same amount over a 24 hour period. Bins are available from 400# capacity to over 1000# capacity.