uriedog Here are a couple pictures of my Dickinson heater mounted in my boat
The chimney provides both fresh air for combustion and exhausts the combustion products. It is double walled and uses a special cap shown below.
Inlet air goes in under the bottom bell, and the exhaust goes out from under the top bell. When sailing and not using the heater we covered the stack by adding a stainless steel bowl with a single hole drilled in it.
This kept lines from getting tangled in it and large amounts of water, that was washing over the deck from entering. You can see the bowl just above the front of the window on the starboard side.
You don't need to go up on the roof to remove the stainless steel bowl each time you want to use it, if you think it is needed to keep rain out while driving your TC. Add a series of holes in the back half of the bowl that I used to allow the gases to enter and exit. We had an earlier version that worked this way.