[Greenbuilding] U-value of single pane plus wood-frame storm window

[Reuben Deumling]

I've stumbled upon an interesting problem. The institution that rebates home
energy improvements here in Oregon is balking at paying out their
$2.25/square foot rebate for storm windows because they were not installed
by a licensed contractor but by the homeowner. <
http://www.energytrust.org/residential/hes/windows.html> Their rules
stipulate tiered rebates based on U-values around 0.3. My question is if
there is a simple , or inexpensive, way to assess U-value. Now that I
acquired an infrared thermometer (Fluke 63) I'm able to measure the
temperature drop across the two panes vs. the drop across the single pane
window in the front door, but this is of course not the same as measuring
U-value. Any ideas?

I am under no illusion that these folks are going to get the rebate, but I
am curious about measuring U-value all the same.

Thanks.

Reuben Deumling