I have an old airco gas furnace, I want to change the thermostat to a RTH 2300, problem is I only have two wires to connect to the thermostat a white and a black and am not sure where to put them? Help

1 to rh
1 to w

Thanks for getting back to me, I have a choice of o/b, y, Rc, R, G, and W. so the W# is no problem but the second wire to RH is, do I use Rc instead?
Thanks in advance

Use the R post
,, the rc is for ac mode

wmproop is correct, just put one of the wires to w, and the other to r. doesn't matter which goes where. If there is a jumper between rc and r, then you can put one wire to either terminal, but for sake of confusion, just put it to r. Wow, I just found a way to make this confusing. Sorry.