I have a client who wants me to remove an old gas fireplace on one side of the room. He will then close this off. There is a gas fireplace in the basement. So this chimney is double flued. Looks like both were wood burning stoves originally. He wants me to cut out a hole on the other side of the existing block work. Dimensions are 34"H x 40"W x 17"D. My concern is carrying the weight of the existing upper block work. I will have to use steel lintels to support the block work. I won't know if this new unit can go into the space given due to where the flue tiles may be. Any advice? Do I just go at this and play by year? I know it is possible to achieve what he wants he just may have to change unit sizes.