The 21 cm brightness temperature \delta T _ { b } fluctuations from reionization promise to provide information on the physical processes during that epoch .
We present a formalism for generating the \delta T _ { b } distribution using dark matter simulations and an one-dimensional radiative transfer code .
Our analysis is able to account for the spin temperature T _ { S } fluctuations arising from inhomogeneous X-ray heating and { Ly { \alpha } } coupling during cosmic dawn .
The \delta T _ { b } power spectrum amplitude at large scales ( k \sim 0.1 Mpc ^ { -1 } ) is maximum when \sim 10 \% of the gas ( by volume ) is heated above the cosmic microwave background temperature .
The power spectrum shows a “ bump ” -like feature during cosmic dawn and its location measures the typical sizes of heated regions .
We find that the effect of peculiar velocities on the power spectrum is negligible at large scales for most part of the reionization history .
During early stages ( when the volume averaged ionization fraction \lesssim 0.2 ) this is because the signal is dominated by fluctuations in T _ { S } .
For reionization models that are solely driven by stars within high mass ( \gtrsim 10 ^ { 9 } M _ { \odot } ) haloes , the peculiar velocity effects are prominent only at smaller scales ( k \gtrsim 0.4 Mpc ^ { -1 } ) where patchiness in the neutral hydrogen density dominates the signal .
The conclusions are unaffected by changes in the amplitude or steepness in the X-ray spectra of the sources .