Spear Anti-Clinker Heater
Pattern A scooped air through a hood on top of the car, carried it down to the bottom of the stove through a pipe, up through the casing air-space thence delivering heat through a pipe the length of the car with registers at each seat.
Pattern B operated in a similar fashion except that the heat was delivered directly into the car through openings at the bottom of the stove.
Pattern C was similar to Pattern B except that instead of an independent pipe to deliver the air to the stove, it brought it down through a casing around the stove's smoke pipe (a much better heat exchange technology).
Pattern D was totally dissimilar to the other three. Instead of the outside hood to bring in air, a vent at the bottom of the stove allowed air into the casing, which was delivered out again at the top.
The first three patterns of the Spear heater would be much like a modern forced-air heater, except that what forced the air was not an electric motor, but the vagaries of air scooped into the car by its movement.
In the case of either of the first three patterns, a Spear heater should be identifiable by the cylindrical air intake on top of the car with the stovepipe protruding. Here's an artists conception.
Pattern D would not be discernible from outside the car.