'a fervor' is correct and usable in written English.
You might use it to describe an intense feeling or emotion, as in the sentence, "The crowd was filled with a fervor of excitement for the upcoming game."
Liverpudlians have always sung this song with a fervor.
Israel will fight Palestinian terror with a fervor.
Gass defends the border between life and art with a fervor few writers can summon today.
This time, the arena was evenly split, and the Knicks fans roared with a fervor.
Suddenly, ordinary homeowners developed a fervor for furniture, carpets and decorative themes.
My dad taught me how to throw a softball and imparted a fervor for college football.
Americans have embraced degrees with a fervor generally reserved for bologna or hot dogs.
These beliefs gave to his speeches a fervor that could not be stilled by criticism.
Stef-fee!" with a fervor that could be heard around the semiempty stadium.
Despite his broad interests, he pursues each with a fervor, often to uncharted depths through his independent research endeavors.
Additionally, Blank says, he wants the students to develop a fervor for public service and giving back to society.
