What you need to know is the gross heating/energy requirements for the application. There are a variety of factors that affect this. Attached is an example of what to consider. Once you have this, then you can let your burner supplier know your requirements.
Burners are rated for a maximum capacity and then you can select based on your need. There are also a variety of burner styles, so your application specifics such as temperature, flame pattern requirement, heating chamber construction, etc., will be equally important in your decision.
Hope this helps, I work for a burner manufacturer. Let me know if I could offer more.