Question: is fuego masculine or feminine?
Answer: no, you can't change the word fuego into femenine... and even though you were describing the house fuego is a noun not an adjective... you can say "Mi casa esta en fuego".... a feminine syn of fuego would be "llamas" and it has to be plural in this sentence.. "Mi casa esta en llamas"... and it has to be 'esta' it ...