look up any word, like fuck boy:
 
1.
Man's greatest invention, and a common mispelling of Refrigerator.
Super R-E-Tarded Dog: "Duhhhh, Furnace." - While reading Refrigerator.
by S-u-p-e-r R-e-tarded D-O-G December 07, 2006
 
2.
The general term for the external and some of the internal female genetalia. All of the mons pubis, the vulva, labia and vagina ending with the cervix. So named for the heat it exudes.
I couldn't wait to see her sweet, wet furnace.
 
3.
To fuck-her-in-the-ass.
Tom: "Hey did you see that girl"
Bob: "Hell yeah I'd furnace"
by mcomer87 September 05, 2012