jebatty said:It should be OK but keep in mind that it operates by drawing additional air into the stack. Where ever it is located, there needs to be adequate additional air supply. If it is draws air from a heated environment, then heated air will be going up the chimney and total boiler efficiency will go down. The comments by others are well-taken.
Be sure you check other ways to reduce the draft. Does your boiler have a forced air draft fan? Can you damper that air input?
I already put it in a week agoClosing both dampers 3/4 does not seem to cause a problem. No back draft or leaking doors (new door gaskets).