The housing is typically riveted together. The rivets, along with slots in the heater case, allow for controlled expansion and contraction during heat up and cool down. Some applications require the slots to be removed, which can be achieved for many designs. Stainless steel cases are used in both food and semiconductor applications. The 304 grade of stainless is most common.
Stainless steel offers enhanced cleanliness and a very polished appearance.
It is important to note that 304 grade stainless steel will discolor at a lower temperature than will aluminized steel. In most cases, the stainless case is riveted together as with aluminized steel. There are some applications were the stainless case is welded and polished for superior cleanliness and cosmetic appeal. Those housings are most often supplied without expansion slots as well. This construction is most often associated with either a glass, koramic, or quartz face heater.