I have an atwood hydro flame heater in my 84 shasta class c motorhome. I had an issue with the heater and had to remove if from the camper. The exhaust tube was destroyed with removal. The furnace is a model fa 7920 p . Searching the internet I come up with parts for the 7920-11. I ordered the exhaust tube using that model no. but it is not the same as the fa 7920 p. The tube is larger diameter and offset. Does anyone know where I can locate vintage hydro flame parts.