Spent a little time on wiktionary:

Unlike its neuter synonym wódr̥, h₂ep- is always gendered in descendants. This may reflect the same animate–inanimate (or semantically active–passive) distinction in early PIE that is often supposed for the nouns meaning “fire”, such as h₁n̥gʷnís m and péh₂wr̥ n respectively.

Two main terms for “fire” are reconstructible for Proto-Indo-European: h₁n̥gʷnís and péh₂wr̥. They are usually considered in semantic opposition. The first term is usually masculine and refers to fire as something animate and active (compare Agni, the most prominent Old Indic deity), whereas the second term is neuter and refers to fire as something inanimate and passive, i.e. as a substance.