I'm replacing my home thermostat.old t/stat are coded with numbers for wire hookup.old t/stat is a white rodgers 125-202.new t/stat is coded with letters... how do I hookup new t/stat?? any help is appreciated... thank you.

Go to the furnace, and see how it is labeled. If it has the same letters as the new stat, follow them. If not, you may need to try to find directions for either the furnace or the old stat. Also see the sticky at the top of the forum. You may need to identify what each terminal at the furnace is for.