  The effect of certain simple backgrounds on the Hagedorn temperature in
theories of closed strings is examined. The background of interest are constant
Neveu-Schwarz $B$-fields, a constant offset of the space-time metric and a
compactified spatial dimension. We find that the Hagedorn temperature of string
theory depends on the parameters of the background. We comment on an
interesting non-extensive feature of the Hagedorn transition, including a
subtlety with decoupling of closed strings in the NCOS limit of open string
theory and on the large radius limit of discrete light-cone quantized closed
strings.
