On Dec 5, 5:02*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 biggest heat loss I found with fireplaces is air leaks. Wind can
blow right in sometimes.
Create a negative house atmosphere and feel for leakage. There are
always holes
in the chimney. If you don't want the eye candy of the fireplace, seal
it with
something like rigid fiberglass, "ceiling tiles" Foam board is
illegal, but you can also
use polyethylene insulation sheets. which is semi fire retardant and
does not need covering by
drywall. For permanent seal, insulate and drywall.

R values are varied according to which chart you use. My typical
cinderbock gets up to R 3.5
or more with fiberglass inside the holes.

For the most part, R value usually means inches of dry wood. 1 inch =
R 1.