My masonry, wood-burning fireplace has a fresh air intake on the back wall; it's just a cast-iron plate that slides on rails across a round metal duct, which vents straight to the outside.
This makes it much easier to start a fire, without having to open a window, but it is quite drafty when it's closed - the plate has about a
1/4" gap behind it. Even with sealing fireplace doors, I get a draft in the room. I assumed the draft was coming from the (slotted!) damper, but after getting a top-sealing damper, I'm still seeing it.
Can anyone recommend an outside-air intake that seals well, or is there no such thing? An exhaustive Google search failed to come up with anything.