mm wrote:

Would a non-contact thermometer be of any value?

Sure. With 70 F house air and Tw and Ta wall and outdoor temps and
a slow-moving R0.67 indoor wall airfilm resistance and an Rv wall
R-value, we have this, viewed in a fixed font:

Tw
R0.67 | Rv
70 F ---www-------www--- Ta
------------
I = (70-Ta)/(Rv+0.67)

Tw = Ta+IRv, makes Rv = 0.67(Tw-Ta)/(70-Tw).

For instance, if you measure a Tw = 67.5 F wall temp with your $50 Raytek
MiniTemp when it's Ta = 30 F outdoors, Rv = 0.67(67.5-30)/(70-67.5) = R10.
This works for windows too. It's best done before dawn, when the outdoor
temp is changing slowly.

Nick