Heater in the bathroom comes pre wired for 900 watts but can be converted to 1800 watts. So at 900 watts plus the 1600 watts (bedroom heater) that makes 2500 watts or 15 amps. And I could put in a 15 amp breaker. BUT does code require the circuit to be a 20 amp because 1600 watts plus the 1800 watts ( that could be converted in the future even thought now it is 900 watts ) I am using 12/2 wire now next question is if I do use a 20 amp with 2500 watts and 12/2 wire is this wrong because it should be a 15 amp circuit

You're confused. And your questions aren't code questions. Whatever appliance (heater) you use, you need to supply the correct amperage circuit That's not a code issue, it's merely a wiring requirement. And a 20 amp, 120 volt circuit is maxed out at 2400 watts. You don't want to run any circuit maxed out, it's just not wise. If you decide to wire the heater for 1800 watts, it will need to have a dedicated circuit... just for the heater. DON'T CONFUSE CODE WITH COMMON SENSE!

And PLEASE DO NOT start a new thread to continue an existing conversation!

Keep it in this thread:
https://www.askmehelpdesk.com/electrical-lighting/code-240-volt-heating-circuit-268765.html

Hopefully a mod can lock this one to keep things clear.

exak, you said "2500 watts or 15 amps"
Actually, 2500/240 volts= 10.41666 Amps.
Volts X Amps Equals watts. Good Luck