This paper describes Direct Numerical Simulations (DNS) of a low speed channel flow with strong heat transfer in the normal direction. The Reynolds number is of order 180 based on the channel half-height and the mean friction velocity. The low-Mach number approximation is applied to study the effects of density variations on turbulence. The data support the validity of the Van Driest (1951) transformation and suggest that the additive constant in the log law is a slight function of the heat flux parameter. A semi-local scaling is shown to be efficient for the stream wise turbulent fluctuations but not for the normal and spanwise turbulent intensities. Temperature fluctuations scale with the local mean temperature gradient.