  Tunneling of the spins in the Fe$_8$ molecular magnet from a metastable
ground state to an excited state is accompanied by a decay of these spins to
the global ground state, and an increase of the crystal temperature. We
measured this temperature using two thermometers, one strongly coupled and the
other weakly coupled to the thermal bath. We found that the temperature
increases to no greater than $2.2$~K. This upper limit agrees with the flame
temperature derived from deflagration theory and previous measurements. In
light of this temperature increase we re-examine the Landau, Zener and
Stuckelberg (LZS) theory of spin tunneling in large Fe$_8$ crystals.
