It happened at a complex on Bissonnet at Lugary around 9:45pm Thursday.
Firefighters say the fire started on a mattress in an apartment on the second floor.
After seeing the flames, the renter threw the mattress out a back window.
That caused what firefighters thought was another heavy fire.
"When we arrived we had heavy fire coming from the second floor and what appeared to be heavy fire on the first floor," said JC Seamans with HFD District 68. "But it was actually just the mattress burning on the bottom."
Nobody was hurt and arson is investigating the cause of the fire.