30" is a good general rule, but the exact height for you will depend on your height, where you stand, how far you lean forward while cooking, depending in part on where the hob is.

To be sure, you can make a cardboard mock-up of the perimeter of the hood; try varied heights (and also different depths) to see more accurately how low you can put the hood without knocking yourself out on it while cooking.

I'm 5'6" and my DH is 5'11". We mounted ours way too low (hey, it was my first DIY-designed kitchen and my first range hood, LOL).

Because of this, when we replaced our range hood this time, I picked a model that has a higher front. This one, the Zephyr Typhoon AK2100, is 26" above the range/counter top, as measured at the front. DH finds it low and has to stoop a bit underneath to taste something 'in the pot'. 30" would be much better, IMHO.

Be aware that the higher you mount your hood, the more you need to pay attention to cfm's and capture area. This is especially true if you've got the kind of range/rangetop with high-powered burners in the front instead of the rear. Most 24" hoods don't extend far enough out to completely capture the smoke/steam/grease from such burners - so you either get a 27" deep hood, or need a more powerful hood to compensate.

Many appliance manufacturer "recommendations" for hood heights especially over powerful gas burners are really building code mandates and aren't to be trifled with if there is a good possibility the building inspector will decide to come calling for a look at the finished work.
The minimum height is usually worded in the codes something to this effect:
"From the COOKING SURFACE (this means "the interior surface of a nominal thin frypan resting on the grates of a gas rangetop or the surface of a ceramic smoothtop) to the range hood shall be a minimum of 30 inches".

From what I have been reading, 30-36" above the range top is pretty normal but the higher you go, the more important the surface area and blower power (CFM) become. If I've misunderstood this I'm sure someone here will correct me, and that will be fine. :)

Modern Aire, which uses Fan Tech inline blowers or Abbaka roof mounted blowers, recommends the hood be 6" wider than the range top. The blower speed (CFM) should be 1/100 of the total BTU produced by the combined burners. And here is what they say about hood height:

"Modern-Aire's minimum hanging height is 30" above the cooking surface with a maximum installed height of 36" above the cooking surface. Modern-Aire recommends hanging your vent hood 32 - 34 inches above the cooking surface for optimal performance..."

I recall reading where one person had his hood height more like 40" because he was tall, but had good surface area for vapor capture. So apparently mounting higher than 36" is a possibility, just not the norm, and you have to provide enough blower power and surface area to capture the fumes.

As an aside, an appliance guy told me that to properly use a hood, you should turn it low on right after you turn on the burners to create the air current before you have created fumes and vapor. He said that doing so does a lot to make up for less blower power. If anyone has a comment about this idea I'd love to hear it.

That appliance guy was right on. It takes time to create a smooth air flow up and around the cooktop; turning the hood on early gets that started before the cooking effluent begins finding other (sub-optimal) paths around your kitchen...

"I recall reading where one person had his hood height more like 40" because he was tall, "

Hmm. I'm also tall. My solution was to relocate the cooking surface up high enough that the hood didn't need to be so far away from it.

Maybe my experience can help.

Mine liner is mounted a whopping 58" above cooking surface. It was done by a contractor for aesthetic reasons, and combined with just a 500 CFM blower and short, narrow, insufficient FanTech liner is obviously not great when I'm searing fish on a cast iron pan. I've lived with it for 4 years, though, cooking frequently, so
It hasn't been unbearable.

The local inspector did come calling. (Spec home.) He approved it with a warning to me that this wasn't going to be a great situation as at as smoke/grease capture, but I was inexperienced and there was no way the large marble archway above my stove was going to be demoed and rebuilt in my brand new home.

Now it's being demoed and rebuilt ;) Not because it wa totally insufficient. The only time I had a problem was when searing/cooling fatty fish at extremely high temps on a front burner. The demo is part of an overall kitchen facelift.

I'm still in love with the tall, high, dramatic arch above the stove. This time, though, I have a great contractor and a couple knowledgeable people to consult with. We're lowering the archway and therefore the liner inside by about 6", so it's still way "too high" at about 50-52" above cooking surface, but that's what I want aesthetically.

We'll increase the CFMs to 1250, widen the duct work and roof cap to 10", get a much wider insert (considerably wider than my 36" range), and either side of the insert will be curved stainless steel to create a "bell" type shape for better capture. The idea is that the smoke rises and rolls along this curve for better capture.

Will be done in about 6-8 weeks.

In commercial settings, the bottom of the hood is typically at 7 feet from the floor. This clears most all cooks' heads. However, such hoods are generally much larger than the surface area of the cooktop over which they are mounted.

The extreme case I've seen advertised is a perforated ceiling acting as a total room hood. One can imagine what would be the condition of the area above the perforations if the effluent were only evacuated without UV lamps to break up the grease into simple molecules. I'm unclear whether the ozone is evacuated or filtered. These may be more suitable for baking operations than barbecuing operations.

kas