Great discussion on NADCAP  in today's Heat Treat Forum. Lucifer Furnaces is also asked..."Can you build a NADCAP furnace?"  In short:  furnaces aren't certified, companies are.  If your company wants a NADCAP certification, or accreditation, your company needs to document your process.  What you might need to show is that your heat treating chamber is uniform +/- a certain temperature range...  There are certain uniformity specifications you may be required to meet.. for example AMS 2750.  It's important to communicate to whomever builds your furnace if you need to meet uniformity requirements.