Try the same with a RED and a BLUE card. Still rough, but possibly closer - there really is no way to tell how much IR is being tossed around.
Run-of-the mill window glasses do not have much of an effect on Infra Red radiation. The other end of the spectrum - Ultra Violet - IS absorbed rather efficiently - that is why it is difficult to get a sun tan sitting in front of an ordinary window. Other materails, plasics, quartzes are used in te manufacture of UV lamps.
Your best bet would be to visit the fiter manufacturer's catalogs - B&W in particular publishes spectral transmission graphs of their filters, and choose from there.