There is a standard calc somewhere for shattering a door. Funny enough that may actually be OOT depending on composition.
Edit:
Here it is. The lowest end is >500kj, so doorbusting is too high. These calcs do all assume solid core doors though, so maybe you could downplay the feat enough if it was an interior door or something.
Edit 2: Zagoor's page actually seems kinda misleading.
This is very much not "exploding a door," as the file puts it. His feats vs doors seem to just be knocking them down, which only requires surpassing the strength of the locks/hinges/part of the wall where the door attaches, as opposed to shattering a big chunk of wood.