Originally Posted By: rsummers
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Couldnt find any resent posts so here is one. You need 1 sq" of area for every 1000 BTU"S of fule input. So a 100,000 btu furnace would need at least (2) 4x14 openings placed with in 1st (12") of the floor and ceiling. One high and one low. I always make it a point to make sure that they are not covered up or clogged with dirt during an inspection.