Renovating 250 year old house to Energy Star standards.Trying to figure out how to insultate massive fireplace - 10' x 8' on first and second floor. Got the draft stoppinng between floors done and know how to draft stop in the flues for the decorative fireplaces. Will have a metal cap on top of chimney which vents the one working fireplace.There are 3 other flues that will not be used, but those fireplaces will be exposed for decoration. Brick has no R- value so HOW DO I KEEP HEAT FROM ESCAPING THE HOUSE THRU THE BRICK INTO THE FLUES AND THEN RADIATING BACK OUT THRU THE ATTIC AND THE CHIMNEY?

Excuse me? Brick has "no R-value"?? Brick was used for YEARS AS an insulator. It isn't used any more, because it fails to meet modern standards...but "NO R-VALUE???" Brick has an R-value for each 4-inch thickness ranging from 0.11 to 0.20, not very much, but it an't nuthin'.

I think trying to "insulate" your fireplaces will be an exercise in chasing your tail. You would be trying to stop the very functions that the chimneys are meant to do. It's an old house, and that is one of the things you'll have to "live with". Applying 2009 standards to an 1760s house was never said to be easy...or even possible.