We are adding a 4 season sunroom onto the house. I have a Tempstar furnace and need to know how many square feet it is rated to heat. I can't find a model number on any of my original paper work apart from "N9MP 2075B12A2" which means zip,nada, nothing to me. Help please.

There is a tag on every furnace required by the federal gov. It states all the info you need to know like btu voltage etc.

The proper way to find out the BTU's needed for the room and if your unit will do that with the rest of the house along with the new addition is to do a manual J. This is a rather complex program but it is very accurate.

Now there are other items like Rules of Thumb etc but a sun room tosses many windows/glass areas so the easy calculation never works under these circumstances.

Here is a short form.

http://www.mrhvac.com/loadcalcshortform.htm