Horace- the plate is just a round piece of lightweight sheet metal, slightly more in diameter than the intake to the squirrel cage on the blower. It's attached to the blower housing by a single screw, which allows me to pivot the plate infinitely between fully closed to fully open, and holds the plate in place.
Originally, I set the blower by feel (read: wild guess
), using the flame height as a reference. Last year I spent the roughly $30 and ordered a Dwyer Mark II manometer, mounted it to the wall behind the stove, and followed the Harman manual to set the barometric draft and blower. If you need the manual, you can download it from Harman's website:
This link is broken, either the page no longer exists or there is some other issue like a typo.
. It's not long on details, but it gets the point across.
The idea of dialing back the blower rpms instead is kinda growing on me
, but I have not actually tried that yet. That might be one of my experiments later this year...