Dear Friend,
I would as, before you put cob on etc, whether you would consider the following two upgrades to your system.
1. Putting a copper water coil around your inner burn chamber vertical tube to heat the water to you home
2. Creating an air-intake tube from outside your house so that air is not taken from within the house.
Not sure if you are able to do this, or have the will to do them, but it would be relatively easy to do them NOW before enclosing in COB than deciding to do them later.
Yours,
Madagoo
