Closed Loop

The combustion process is a combination of fuel heat content in joules, Btu/unit of fuel, etc. Each type of fuel that uses combustion to release heat requires a certain amount of required combustion air and in most cases excess combustion air to complete the process for air quality and efficiency. The calculation needs to be precise as too much combustion air will cool the process and cause one state of pollutants while insufficient air will not allow complete combustion and cause another state of pollutants, carbanization of the equipment, etc. Unless you get it right, the heat content available in the fuel will not be realized, hense, the efficiency test for your equipment. You need to select your fuel type and find the manufacturer of the equipment that you are using. The settings for your burner will be provided. Combustion testing meters are available to prove that you have set up your equipment properly. Temperature is just one parameter of the combustion process.

Set point is a value at which you want to keep a process steady, between your upper and lower ranges; thus your set point will be a numerical value (ie. 21° C). Perhaps if you refine the wording of your post I can be more helpful. I just don't understand what exactly you're trying to ask.