I believe my fireplaces have an odor afterwards also, although not very strong. I only burn cured oak. Is that what you use? I wonder if it could be the wood. I previously owned an older home (40 yrs.) that had a fireplace in the living room and one directly below it in the basement and recall just a faint odor of the wood. I just cleaned it out when the ashed were cold. The cover I made for the new house is made of wood and has rubber gaskets around the edging and strong magnets to hold it to the metal facing of the fireplace box, which also has glass doors attached to it. It works well at keeping drafts out - until I burn a fire in one of the other fireplaces. My spouse and I are going to try leaving the glass doors closed when the fire is burning, but I don't think that's going to solve the problem. Your odor though, I wonder if it's just the wood.