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.

Thanks,
mike

I suppose it depends on what code you are on but the "1 hour" fire rating usually only applies to dwelling space above a garage.
I have asked about fire dampers myself and that is what I hear. They use garden variety hollow core passage doors between the garage and mud room or laundry room here in Florida.

mike,
302.4 exc#3 of the calif bldg. code(1997 u.b.c.)states no damper required if ducts are 26 guage and no openings in the garage.

pwood,
I don't have the building code so let me ask some more questions:
-if the ducts are thicker than 26 gauge, is that OK?
-By no openings, do you mean that there are nor registers in the garage?

Thanks,
Mike

mike,
the 26 guage is a minimum thickness and no openings are allowed in the garage.no registers or returns,only the unit with supply and return directly to and from the house.