I have a 14 X 40 wood frame shed I am turning into a cabin at my property. I bought an old vigilant and got it installed over the weekend. I have 17 or 18 foot chimney sticking up quite a bit above the roof. I haven't done a proper fire in it yet, just burned a bunch of cardboard the chimney pipe came in. Its drafting great. Neat to open the griddle and see the fire getting sucked into the flue. Anyway I noticed a little set screw is missing on the lower left side you can see in to the fire. I would think that might be for coal use and that for wood it would let in too much air. Should I plug it? Any idea if so what size it is? Definitely threaded, at first I thought someone had drilled a hole in it. Don't worry about the photos, I am 36 inches from the wall and will put up drywall and a heat shield before giving here a real go.