I have a 3 season room that is 22-12 with 13' ceilings. How big of a heater do I need to heat it in upstate NY?

Speak to your local building/plumbing inspector. You have not provided any info regarding if your room is facing north or south. Or the insulation...or the window size, current ventilation, elec or hot water heat, etc,or many other factors. The inspector will have the needed tables to determine what is best for you. And it is free.