A method of converting naphtha is disclosed. The method includes heating the naphtha in stages in different heating units. The naphtha is vaporized in the first heating unit. And the vaporized naphtha undergoes the largest temperature change of the process in the second heating unit. A third heating unit can be a part of the reactor. The reactor includes a catalyst which is contacted with the pre-heated naphtha to convert it to C2 to C4 olefins.