I will be installing an insert into my heatform fireplace soon. I know I need to cut out the heat exchange tubes and damper for a full liner. With this project I plan to reface my fireplace with veneer stone, its currently brick. My question is can I brick the vents in the fireplace so I can stone over the whole thing? I will be insulating the firebox so to help with heat loss as much as possible. With the fireplace not being functional any longer, is it safe to cover the vents?