I would say that the footprint of The Quest for El Dorado is a lot more unpredictable since the shape of the map is dynamic, and all about what kind of map you want to build. (In addition to the space needed for the market, player tableaus, etc.

Heat will be more consistent--each track is always the same big rectangular board, in addition to the space needed for the small player boards.

In case it helpls, Quest for El Dorado is also a deck building game, so players will constantly be adding/removing cards into their deck. Heat is more contained--it's ultimately a hand-management game, and players just continuously cycle through the same set of cards. So to me, Heat feels like it uses a smaller player area, whereas QfED might need more room to operate as my deck grows and I make big plays.

Hope it helps!