Most here probably have no idea what a KTJ304 is, as (I think) they're about 40 years old now. This is a pre-catalytic stove, and the cross-section in the manual does indicate it's just a wide open box, open to the chimney, if we put any faith in that sketch.
Do note the manual calls out inspecting the chimney TWICE per month, and cleaning if necessary. The capitalization of TWICE comes right from the manual, that wasn't me. By comparison, most of us today are running stoves that could go a few years between cleaning, although a yearly inspection is always recommended.
Paging
@BKVP, he may be able to help, but I'd really consider ditching that antique and finding something better, if you can swing the budget. They've improved an awful lot in the 40 years since that model was popular.