Sheet metal stoves should be examined frequently for weak, burned out spots. They warm up more slowly than sheet metal stoves, but the thicker wall section lasts longer. These units are suitable for continuous use. High quality models will have firebrick lining in the combustion area. It provides a stove that warms up slowly, retains heat well, does not warp and lasts for many years.
Cast iron is relatively brittle and is subject to cracking if handled roughly.
For this reason, you should carefully inspect new and used cast-iron units for breaks before using them. Firebrick or ceramic liners may be used in any of the three stove types. Liners add mass to the stove and tend to spread heat away from hot spots in the fire. This promotes more uniform heating and prolongs the useful life of the stove. Liners also lengthen the time between the starting of the fire and the heating of the room.