Would this be too large for a 300 ft. shed?

Great question. This stove is approved for 400 sq. ft. Up to 2,200 sq. ft. The 300 sq. ft. shed would be too small for this particular unit. If you have any further questions or need further assistance, please feel free to reach out to one of our experienced customer service representative and they would be happy to assist you. Thank you and have a wonderful day.