  CARMENES has been proposed as a next-generation instrument for the 3.5m Calar
Alto Telescope. Its objective is finding habitable exoplanets around M dwarfs
through radial velocity measurements (m/s level) in the near-infrared.
Consequently, the NIR spectrograph is highly constraint regarding
thermal/mechanical requirements. As a first approach, the thermal stability has
been limited to \pm 0.01K (within year period) over a working temperature of
243K. This can be achieved by means of several temperature-controlled rooms.
The options considered to minimise the complexity of the thermal design are
here presented, as well as the transient-state thermal analyses realised to
make the best choice.
