Gas fireplace insert expansion

Yes just need to measuring opening in exsisting spot and When you put gas fireplace venting with 2 pipe on the chemney 3 or 4 Inch depend shere Is fireplace located basement or FIRST floor

The most important step is to review the manufacturer’s installation manual for the new fireplace and confirm that the size of the existing exhaust/vent pipe meets the requirements for that unit. If the current vent size is sufficient, it may be able to be reused. Otherwise the venting system may need to be modified. Another factor is the gas supply. If the new fireplace has a higher BTU rating, the gas line may need to be checked to make sure it can provide enough gas for the new unit. Clearances around the fireplace should also be verified to make sure the existing framing and surrounding materials meet the requirements of the new appliance.