On Dec 5, 4:02*pm, mike wrote:
I've got this red brick fireplace taking up half a wall.
Capped the chimney decades ago, but it's still siting
there conducting heat outa' the place thru the bricks.
How would one go about calculating the "R-value"
to estimate the heat loss. *Any useful rules of thumb?

Trying to decide whether to put insulation over the bricks
on inside or outside or both.

The fire box and chimney will convect in cold, I use a piece of
foamboard to seal my firebox up, mine is removable, held in place with
magnetic tape and painted dark, it helps alot.