What you are talking about is staggered height cabinets. Its a matter of taste: some people like it, some people don't. In some kitchens, I think it looks fine. As for a single cabinet being higher over the range hood, I tend to think it looks like the cabinet was moved to make the range hood fit, because I've seen people do that when they get an OTR microwave: it hangs down too low because its bigger than the old hood, so they pop the cabinet up to compensate.. However if it is part of an overall design of staggered cabinets, it can look nice, and look intentional.

Hello Houzz Community! I found this thread when Googling a similar topic. I'd like to replace my under cabinet hood with a wall mounted hood, and yes I know I have to remove the cabinet above the current hood which I'm fine with (see photo). My existing under cabinet hood vents out the wall to the side of my house - see photo, and note the vent is not blocked by those shrubs, there is space around it, you just can't tell from the angle of the photo :-) So my question is....can a wall mounted hood be installed to vent out the existing vent in the wall, or does a vent need to be created in the ceiling? Also, what type of professional can help answer any related questions I have about this? Would I ask the wall mounted vent manufacturer? Or a handyman? Thank you in advance for any guidance! I am a newbie homeowner and am learning as I go, so truly appreciate you taking the time to share your knowledge with me!

The OP wrote: "- We can have a 10" duct, but can not install external blower because there will be at least 3 ninety degree turns for the duct to go through the roof (kitchen is on the 2nd floor and there is another floor sitting above the kitchen)." I must have missed this thread. Just what effect is being assumed here such that the location of the blower is affected by the three 90-degree bends, so long as none are right at the blower. (Hint: Pressure loss capabilities of kitchen hood system blowers are minute factions of an atmosphere. Due to this, pressure losses on the blower intake side and pressure losses on the blower output side have the same effect, particularly when a 10-inch duct is to be used for a sub 1000 CFM requirement.) If one wants [relative] quiet in an open area. the blower should be remote from the hood and a silencer placed in the intermediate ducting. As widely noted here over the past decade or so, rated CFM and actual CFM differ by a significant factor, and one cannot address kitchen ventilation with only hood system parameters. The make-up air system parameters are equally important.

Sorry, but I would exchange it for a hood that is deeper than 19". That is really shallow, as you are finding. Proline does sell 24" deep 30" wide hoods, but even 22" deep would be an improvement. Better to exchange the hood for a deeper one than jump through hoops to try to jerryrig it to be deeper which may not be fire safe over a cooktop. Regarding the duct, my understanding is that the fewer the turns of the duct, the more efficient is the exhaust, but I understand your point about accessibility. Still, you shouldn't need to access the duct after the initial installation, so I would vote for the option without the turn. Perhaps some experts will chime in.