I have 4 wires, red, yellow, white, green.. took off the old round thermostat because it was cracked.. it had no letters labeling the wires! I bought a Honeywell simple thermostat for heat only, it has 2 terminals W and R.. Its cold here in Chicago and I really can't afford a heating call.. HELP!

There is a color code for thermostat wires, and if the original installer followed that you would hook the red wire to R and the white wire to W. You only need R and W for heat.

Hope this helps,
WallyH