How should element spacing be specified for industrial heating elements?

Set element spacing from allowable surface load and the furnace's measured thermal field, not from equal-pitch layout. Work back from power, sheath diameter and material to a maximum watt density, then derive the closest acceptable pitch so adjacent sheaths do not overheat, oxidise or degrade insulation prematurely. Tighten spacing at corners and around work fixtures that shadow heat; widen it in open zones. Keep thermocouple or control sensors out of direct radiant paths. Confirm the final pitch by thermal mapping and freeze it, with tolerances and duty conditions, on the approved drawing.