I am installing a woodburning stove in my lounge. There is already a fireplace with a back burner installed. Have removed the cosmetic brick surrounds to reveal the breeze block chimney and lintel. Good news the lintel is high enough for the wood burner. Bad news, the chimney hole is not wide enough for the burner. Can I widen it without moving the lintel? If so any tips, dos and don'ts. The house is only about 18 years old so chimney and liner are in good nick.