A 200 sq.ft. room may require roughly 1,200 to 2,000 watts depending on insulation, windows, ceiling height, climate, and other heat sources. Many wall heaters for rooms around this size fall between 1,500W and 2,000W. Check the manufacturer's rated coverage before selecting a heater.
Yes, one properly sized wall heater may be enough for a 200-square-foot room. The heater's rated wattage and room coverage should match the space, while factors such as poor insulation or large windows may increase the required heating capacity.