  In this numerical study on Rayleigh-B\'enard convection we seek to improve
the heat transfer by passive means. To this end we introduce a single tilted
conductive barrier centered in an aspect ratio one cell, breaking the symmetry
of the geometry and to channel the ascending hot and descending cold plumes. We
study the global and local heat transfer and the flow organization for Rayleigh
numbers $10^5 \leq Ra \leq 10^9$ for a fixed Prandtl number of $Pr=4.3$. We
find that the global heat transfer can be enhanced up to $18\%$, and locally
around $800\%$. The averaged Reynolds number is always decreased when a barrier
is introduced, even for those cases where the global heat transfer is
increased. We map the entire parameter space spanned by the orientation and the
size of a single barrier for $Ra=10^8$.
