Saturday, October 20, 2007

Fake Air Returns: Watch Out

I remember reading a post at HVAC-Talk a few years ago when someone wrote that a contractor just cut a hole in drywall, installed a return air grill and claimed that it is exactly what it is supposed to be - a return. Long and heated discussion followed (HVAC-Talk expires threads, so the source is no longer available), with polar opinions being a) yes, it's acceptable and b) not at all, you must provide the path.

I've seen grills leading to dead spaces a few times afterwards, which makes me think this is not an exception.

Now that I'm learning framing - well, turns out that the building code explicitly calls for installing what is called fire blocking: two-by stud material that runs horizontally from stud to stud - every 10 ft measured vertically in stud bays. Fire blocking interrupts the upward flow of flames and heat.

Two lessons:

  1. There is no easy way to install an air return in a room;
  2. There is no easy way to wire anything - studs (at the minimum) are horizontal obstacles, fire blocking (at the minimum) are vertical obstacles.


  1. It could be worse. You could live in a mobile home, where cold air return is grates over (or in) the door of each room. The furnace just sucks air from the room it's in, and that's supposed to pull air from the far end of the house...

    I really do like my mobile home, but HVAC is not its strong point... ;)

  2. Timothy: it could be even worse - you might have no grates in or over the doors at all, just about an inch of open space below the door - in a permanent house.

    No houses I've lived in in last 10 years had dedicated air return channels, I guess this is something that only can be encountered east of Chicagoland.