Interesting guys! For now we have put the air intake into the crawlspace up to our hearth. If we ever want to actually hook it up it will be there. And my hubby put a vent on it to the hearth so it will have air there if needed. The tile guy is going to make a piece of tile that will fit on top of it when we don't want to use it. I am sure it will still be a little drafty but it will at least provide a bit of air if needed. We recessed the vent (a expert here suggested that) so that the tile will fit right on top theoretically. =) Will see how it all works out. Get the rock installed tomorrow. Can't wait to see the hearth! I've been looking at a open wall for weeks.....will be nice to have it covered! Cement board got put up today and it already looks better! 
