Trying to make small jersey cakes for a party
I have done thatTake two coat hangers apart and twist the ends togetherBend it into the shape you want and twist the ends togetherForm your pan with aluminum foil and roll it over the wireThe wire forms the rim of the pan so it doesn't collapseIt is not very sturdy, so you have to be carefulSlide the rack out of the oven, let it cool, then slide the cake onto a cookie sheet or other solid surface When I did this it was a banana that perfectly fit the oven corner to corner, just over two feet long, and I transferred it to a board from my bookshelf which I had covered with foilThen I covered the cake with yellow and brown frosting and stuck a Dole banana sticker in the middle.
Go to the attic and cut a piece of cardboard to fit around the open portion of the chase and seal it off thereIf you attempt to fill the space you may create a fire hazardIt will not take much to block that but be careful doing things to fireplaces especially if the home is not yoursIf there were ever a question with a problem and it links to something you did you could get introuble.
Shawn has a pretty good idea but not sure about the clearance on the vent pipe but you can flash it off with metal to sealIf this is a gas fireplace it vents flue gasses up the center pipe and draws combustion air down the outer pipe so only one inch is required for clearance to combustiblesThen you can cover that with fiberglass insulationIf this is a wood fireplace flash with 12 and cover with high temp insulation such as KAOWOOL.
