I moved into a house with an old Whitfield insert. Manual light manual everything but we like it. Thanks to help on here it runs like a clock! I was moving it for a cleaning and noticed the that the flue has ~ a 4 inch pipe going up it for the exhaust. Around the pipe is a massive opening where I can feel cold air coming down the chimney. Large brick chimney. How hot does that pipe get? Could I use regular fiberglass insulation? Ceramic blanket?