That would be fine... as long as you are not exceeding the 40amp timer limits... AND the wiring for the 80amp circuit is appropriate size. What circuit in your place is on a 80amp circuit? Also, don't double-tap the 80amp breaker... good way to cause some problems for yourself.
well its my furnace circuit, and the wire is huge!, dont know the guage off hand but im bettin its 6 or 4, the wire im using to the outlet will be a 10/3, and like i said running pretty much 9-10 amps off that circuit only.
10/3 is adequate for 30amp. How are you making the connection to the existing circuit? Junction box? I hope. And really, you should put a 30amp fuse or circuit breaker disconnect in there to be proper and safe (after the furnace connection).
Let me know if your not following me. I will sketch you a diagram if you need it.