Goschman, your post is kinda vague. Are you saying you bought a burner for propane but want to use it for natural gas? If so you need to provide a description of the burner to get the right advice. I have drilled out an orifice to convert.
Not sure how many BTUs your burner has and how close to the pipe your burner is. As a general matter, your hose should be no less than 1/2" ID for longer runs. Your burner may have a narrower connection for which you can use a hose of 18" or less.