We calculate the radiative heat transfer between two metallic gratings by exploiting the Adaptive Spatial Resolution metod. This technique dramatically improves the rate of convergence allowing to explore smaller separations. The heat flux shows a remarkable amplification of the exchanged energy, due to spoof-plasmon modes. We find a consistent disagreement with some previously obtained results going up to 50% (this disagreement is explained in terms of an incorrect connection between the reflection operators of the two gratings).