What's this vent for?

[tomcrogers]

I'm cleaning my firebox today and noticed a vent on the back wall...there's a little metal door, which if open allows me to see outside (of course there is a screen and some sort of baffle, which can be opened and closed). I don't know what his is for...or what setting it should be on. I do have some problems with smoke coming in the house during startup and cool down...maybe this is part of the problem (or solution)?

Any ideas? I have no clue, so any advice would be much appreciated. Thanks!

 

[elkimmeg]

Today codes require an outside air feed to fireplaces this is what you are describing It was instituted due to modern homes being insulated better and being tighter.
the outside air supply allowed fires to be burnt and prevented smoke spillage. That's not the problem but the solution. Open it up when you burn your fire place

 

[tomcrogers]

Thanks! Should I open the baffle and the metal door...leaving them both open during a burn? I'm afraid the smoke will start spilling out the side of the house...