The goal of the cooktop ventilation is capture and containment. Capture refers to collecting the rising and expanding cooking plume effluent; containment refers to keeping it in the ventilation system until it is expelled outside.

Capture requires that the hood entry aperture overlap the expanding effluent conical plume (which may be bent due to cross drafts). A 22-inch hood may not fully accomplish this at any height, depending on pan size and cooktop burner layout. While the subject is actually complex, one can roughly approximate the plume as an inverted cone with the pointy end down below the cooking surface, and the cone sides touching the pan base (or with gas, the flame diameter, if larger). The cone side angle may be treated as being 10 degrees to the vertical, although this also varies with what is cooking and pan base temperature.

The portions of the cones that rise from all the pans that are being used on the cooktop at a given time that enter the hood aperture are captured. A small amount that would just miss the aperture may also be captured with high enough air flow. What isn't captured is distributed throughout the kitchen or house, and my be removed due to general air flow, before or after its grease and odor load is deposited on surfaces.

Containment requires that the velocity of the air being pulled through the aperture be high enough that any place the rising plume strikes does not reflect the plume back downward such that it escapes from the hood. Schlieren imagery may be found on the Internet showing this effect for commercial hoods with insufficient vs. sufficient air flow rate (velocity times area).

So, in general, raising a hood and expecting the same performance requires proportionate increases in hood width and depth, and increases in air flow rate proportional to the increased hood aperture area to keep the velocity up.

Or looked at another way, one should start by determining what hood size is needed as a function of height (for capture), and what height person is safe from intersecting the hood when bending at that height. When the height that is safe for the expected cooks is found, the hood size can be used to find the needed air flow rate. From this the (higher) blower specified (zero static pressure) air flow rate can be estimated. Many topics on this forum address this subject.

kas

30"-33" distance from cooktop to bottom of hood is considered typical and most effective. VAH's instruction to 27" is too low. People go up to 36", but I wouldn't go above that; you will lose exhaust effectiveness, and it would be a shame to pay all that money for a hood and have it not be effective because it's too high above the cooking surface. Also, a higher-than-3-foot distance above the cooktop looks odd/out of proportion. 30-33" is ideal.

32" distance is what I have. It's absolutely fine. You think you're going to have to duck but you won't. Remember your cooktop sticks out at least 24", so your 22" deep hood isn't sticking out beyond that. Furthermore, after using your cooktop a couple times people get a sense for where the hood is, and don't bang their heads. Relax.

Don't forget when using your vent the key is to stay ahead of the fumes. Start the fans before you need them. We had a VAH and were happy with it. I am sorry I do not remember the install height.