I am trying to install a fahrenheat f2543 heater

Hi, this is very easy for you to do.The 12/2 Romex wire coming in is the power which you know. What you do need to know, is the voltage coming in? Sometimes they will use 12/2 Romex with ground for 220, 240, operation. You need to know if the T-stat is Line voltage 220, or 240 volt. You have to have the same voltage for both for it to control. Reguardless of the voltage, lets say it is in the 220 and up range. You take one of the 12/2 wires, white or black and hook it to the black or red on the T-stat and the white to the other one, red or black. Thats it, you are done! If the T-stat is 2-pole I am sure it is a high, Line votage T-stat. Best of Luck,
Shastalaker7