Of course all openings will radiate heat, but you want to maximize the pressure differential across the core. Without wool tufts or a magnahelic (sp) gauge you can't possibly know. Sure you could compare your IAT's before and after but that will be dependent on a number of factors well beyond our control.
There are 2 other articles in the series
Part 2 and
Part 3. I would really like to see someone provide a case for a hood with evidence.