I've worked in a few houses, all built in the '80s that had the furnace in the garage. Typically, the return air would enter through a built plenum benaeth the unit, and there would be ducting abouve it going back into the house. My question is this: if the house requires 1 hour seperation from the garage, why were there no fire actuated dampers on the return and supply of these furnaces? Was the one hour seperation not required back then? Is there an exception for residences?
BTW, these were all located in southern California.