I have a question on the 80/20 lever. What exactly happens behind the front of the furnace? I have the 526 and I would like to coble something up to do the same thing with it that the 2900/4000 do with that lever. I know that it redirects the air somehow from under the grates to above. Just curious how. So if anyone knows, and can explain it, pictures would even be better, please by all means. I would greatly appreciate it.