We report a resonance-driven convective heat transfer enhancement downstream of a natural convection boundary layer that is perturbed by a moderate impinging jet. Flow resonance is experimentally and numerically confirmed between the boundary layer and a periodic flow driven by the unbalance of jet momentum and buoyancy. When the oscillation frequency in the impinging region is a submultiple of the characteristic frequency of natural convection, downstream heat transfer enhancement E from the baseline of natural convection exceeds 40%. In contrast, further increasing the jet momentum fourfold yields E<20%. The results support the development of efficient heat transfer enhancement methods.