From what I can make of my FURNAS family tree is that an alternate spelling is FURNACE,FURNASS, and FURNESS. I always check all 4 spellings when I am looking for someone. I will say this though, my grandfather's sister (Laura Furnas Knapp) and a few brothers (Oscar, Alfred, and Charles C.) all lived in St. Louis and surrounding areas at some point, between 1910 to 1930. Some moved on to California. Charles Chapman married a Leona Acker in 1908 at Linneus, Missouri but he died in Oregon. The father/mother of these siblings (Seth W. Furnas and Emily Moore) lived there in 1910 also.
You may be a descendent of one of these siblings and your last name was mispelled in the process!