30" minimum clearance from range hood to the cooking surface (i.e. the inside cooking surface of a frying pan on a grate over a gas burner) is a common building code requirement (which should be confirmed to apply or not in your area). There may be additional state code safety and conservation requirements for installing a stand alone make up air system with heat energy recovery for your proposed item in your particular state.

More info needed.

This post was edited by laat2 on Fri, Oct 25, 13 at 11:13

Here's what I have over my 36" Bluestar RNB with griddle:
Prizer 36"x27" mounted 36" above burners. 1000 cfm remote on 8" ducting. Works satisfactorily on low speed for most cooking, although when searing or stir frying, a bit of smoke may escape. I think if it was down at 30" it may have been more efficient, who knows? ... I do know it would hit me in the head!
I think with your 42" wide, you should be fine for everything but maybe the smokiest cooking.

This post was edited by ctycdm on Fri, Oct 25, 13 at 11:29

Thanks for the input. I was to concerned about frequently hitting my head being 6' tall. As for MUA, it doesn't appear my jurisdiction has any requirement, so I wasn't planning installing anything. However, there was an unused 6" duct in the wall that vents to the outside that I could use a some point in the future if deemed necessary. For now, I was just planning on cracking the sliding glass door as needed.

The extraction efficiency will be much better if installing the hood just 30" above the cooking surface as opposed to 36".

If you're "only" 6' tall, don't worry, you won't bang your head against the hood. The 6" difference between the hood bottom and top of the head (6' - 36" - 30") will be lost when you bend over the range, especially since the hood is only 24" deep while the range is probably at least 26" deep.

I installed mine at 29" above the cooktop and I'm 6'2"; I can barely touch the hood with my forehead if I lean over the pots.

Moreover, in time one develops a subconscious feeling on how to move around the hood without hitting it.

IOW, install the hood as low as possible and it will be much more efficient at removing grease, smoke and odors.