Hi,this is whisky4,I was wondering if there is ratio that you use to determine the size and how much you can close up the throat of a fireplace to make it more efficentor do you just play it ear,i.e. close it up until it smokes then back off,thank,s

I twist mine shut till I notice smoke then I open up just a bit. When you have it adjusted like this you have to watch it. A slight down draft can fill the house with smoke.

I twist mine shut till I notice smoke then I open up just a bit. When you have it adjusted like this you have to watch it. A slight down draft can fill the house with smoke.
And a CO2 detector near by