How to close off old heatilator ventilation holes

[a2k]

We had this fireplace converted to a stove insert and too much metal from the old firebox inside the chimney was inadvertently cut away, letting hot air from the room go up the chimney through the holes above the fireplace when it's not in use. It's only used very occasionally and the room feels colder than previously, so I can only assume our heat is going up the chimney. Apparently with the type of chimney liner that was installed for the stove, a top damper will not work. Does anyone have any affordable suggestions for closing up those openings above the fireplace or another way to block air from going up the chimney? Because it's now a fireplace insert stove with no accessible space around it, a balloon pillow will not work. Each of the openings are about 7" tall.

 

[FireplaceTreatments]

Fill them with mortar. I'm not a mason, but if I wanted to do it myself, here's what I'd try:

Get some wire mesh and cut it with metal snips jut a bit bigger than the shape of each hole. No need to be precise. Push the mesh into the hole and it will hold itself in place as the mesh bends and the rough edges bite into the stone. Mix some quick set mortar and fill the hole. The mesh will help keep the mortar from falling through the hole. If the mesh wants to fall backwards into the hole when, tie a string or wire to the mesh and have someone hod it while you put the mortar in. Do a couple layers of mortar. You can cut the string or wire off in the first mortar layer and it will be hidden by the next layer.

 

[bholler]

We had this fireplace converted to a stove insert and too much metal from the old firebox inside the chimney was inadvertently cut away, letting hot air from the room go up the chimney through the holes above the fireplace when it's not in use. It's only used very occasionally and the room feels colder than previously, so I can only assume our heat is going up the chimney. Apparently with the type of chimney liner that was installed for the stove, a top damper will not work. Does anyone have any affordable suggestions for closing up those openings above the fireplace or another way to block air from going up the chimney? Because it's now a fireplace insert stove with no accessible space around it, a balloon pillow will not work. Each of the openings are about 7" tall.

View attachment 329650

Pull the insert stuff mineral wool in the smoke chamber the holes cut in the heat form etc then make a sheet metal block off plate to close everything off. Mortaring the holes outside isn't a bad idea either but im.sure premix won't match the original color