Sorry, somewhere in the back of my mind I thought I had replied to you.
He actually went up to Vermont and bought a Chappee to put in his new house in the Waldoborl area. What a hoot. He indicated that the plate was for a coil. He has never seen a coil for one however. If you remove it the use will be self explanatory I would think. I know I typed this all up once before! Anyhow, he circulated water through his oil boiler to keep it from firing, to increase the amount of hot water available on call, and to store some heat as he found that coal was so blasted hot he had to temper it somehow. The coil in the oil boiler went to an electric water heater.
The Calorastat is a great device however. Make sure your doors fit really tight, controlling the air is important. I think he had a baro set up for his oil boiler but none for his Chappee, I am sure there is a setting it is supposed to be at. Maybe in one of the manuals?