I would think these were common items in the day for Model T's living in Frostbite Falls places.
I have a NOS one very similar, however the trap door is gone, but I might have one 125.00 plus UPS email@example.com
How do they work??
Fits over exhaust manifold. A hole is cut in the floor boards to fit the vent. Open the vent to get hot air into the passenger compartment. Works best in closed cars and cars without exhaust manifold leaks.
I have a similiar one on my 24 coupe that I drive in the winter it really puts out the heat