How far should they be above an operating door?

Are you talking about the termination of the vent of just where it runs. Stacks should terminate above the roof line.

Here's how my code book calls it guys (Massachusetts, Uniform State Plumbing Code, 93):

"No vent terminal shall be located directly BENEATH any door, window, or other ventilating opening of the building or of an adjacent building NOR shall any such vent terminal be within TEN FEET horizontally of such an opening unless it is at least TWO FEET above the top of such opening"...

So basically, if your vent terminates TWO feet above doorway and no other windows/ventilating openings above the door... you are all set by code.

Any window/air intake above that door must be farther away than TEN FEET horizontally for you to terminate your vent above the door.

Code in your area may differ slightly... but I bet not by much... so, If you can't meet these requirements... then as Ballenger said... must terminate vent through the roof.

All vent penetrations must be 2" minimum size pipe... and if going through roof... should extend to between 18" and 24" maximum through roof.

Hope that answered the question..

If not, was fun to post this info. Anyway... ;)

If not, let us know what you can... :)

Mark

24 inches above the roof at the point it emerges sounds as I remember also. Chimney stacks are determined by a point of roof a distance away. "Mass" nailed this one for you. I remembered that the stack cannot be within 6 feet of an attic vent or must be above it 2 feet also. I think it may be true for air conditioning units and swamp coolers too.