Best way to stop cold air coming in from fireplace

Question

My house was built in 1967 and has a real working fireplace. The problem is, it allows a ton of cold air into the house. There is a chimney cap (and I climbed up on the roof to verify it still works), as well as glass doors on the front of the fireplace which were clearly made for safety and not sealing the room from cold air. Since cold air was still pouring in I added a chimney balloon.

However on cold mornings I use an IR thermometer and I can see the difference in temperature around the fireplace - it's still letting tons of cold air in. At this point I no longer care if I can use the fireplace for fires (I got an outdoor firepit for when we want to have bonfires and/or make s'mores). What is the best way to stop cold air coming in? Do fireplace inserts effectively seal them off from the outside? I keep searching for info but everything I see assumes I'll be using the fireplace insert to generate heat by burning things (which I don't really plan on doing). I don't want to heat my home with the fireplace, I just want to stop cold air from pouring in.

Answer 1

You can build an inexpensive "plug" for the front of the fireplace. Get some thick plywood cut just barely smaller than the opening of your fireplace. On the back of the plywood attach thick styrofoam or the foam insulation panels cut slightly bigger than the plywood. Attach a handle to the front of the plywood and paint any color you want. Stuff this into the front of the fireplace to keep drafts out.

Answer 2

I would get some plastic sheeting and tape it up all around the front of the fireplace real good so no air comes through. Use good quality duct tape. You could use clear or black plastic. You could also use color plastic for special holidays. Red or Green for Christmas, Orange for the fall, pastel blue or yellow for Spring.