5 ton furnace with a 20x20x1 filter rack screwed onto it, the rest of the opening panned off with sheet metal.
For an extra bonus, 1/3 of the filter rack also panned off with metal!
If more government is the answer, then it's a really stupid question.
And the Delta P is? That had to be some CRAZY static pressure! "But Mr. Service Tech, I haven't had a single problem. It's worked fine since the day of installation."