http://hearthnhome.com/downloads/instal ... II_III.pdf
click on link above, it's the owners manual for a Harman Mark I or Mark III coal stove. When you click on it, wait until the PDF file opens, then scroll down to page 7, section 3.1
here's what it says:
UNDER NO CIRCUMSTANCES SHOULD A MANUAL FLUE DAMPER BE INSTALLED IN THE SMOKE PIPE BETWEEN THE STOVE AND THE CHIMNEY.
then read the bottom of page 6, here's what it says:MANUAL DAMPERS OR “HEAT SAVERS” MUST
NEVER BE INSTALLED IN THE FLUE PIPE. IMPROPER
OPERATION COULD RESULT IN DEATH.
that's the final say in stove pipe dampers of any kind, including baro dampers, on any antique or modern stove, using a recirculating type exhaust design, to extract more heat from the stove. Stoves of this type are already internally baffled and dampened. Putting another damper in the stove pipe on such stoves, risks death from CO backing up into the room and home.
having said that, relying on a damper as such, to get "efficiency" from a stove made in the 1920's, is risking your life and your family's life. We've learned a little since then. These recirculating exhaust stoves should not have a damper in the stovepipe.
Only use a stovepipe damper on a wood stove, or very cautiously on a coal stove, providing the coal stove is not internally baffled already. There are differences between manual damper design for coal and wood stoves. A coal stove damper has holes drilled in the middle and will still pass 20% of total volume when fully closed. A wood stove damper will have no holes in the middle.
Ask yourself why those holes are in the middle of the damper, for the coal stove. Because the CO gases from coal, are deadly.
That's playing with fire, literally. I sleep very well knowing there's no manual damper on the flue pipe of my Harman I. Flue pipe damper SPRINGS do wear out from heat, and then the damper becomes loose and doesn't hold it's adjustment. This $6 hardware store mechanism can kill you, if it blocks the stove pipe on a coal stove, that's internally baffled. Never install a solid damper on a coal stove. The risk is not not worth any amount of efficiency or money you may save.
These tall free standing "oak" style vintage stoves of the recirculating design, fall into this category. Proceed with caution.