I think the gap will look weird. You should get a 42" hood - you shouldn't have any problem finding one - it's often recommended that the hood should extend an extra 3" on each side to improve the capture area so you're all set. In my opinion though the depth of the hood is even more important, so get one that's at least 24" deep from front to back, or even 27".

as weissman said, you actually NEED the 3 extra inches on the sides of the hood. The problem with not having the hood there is not a matter of the grease and other items collecting on the hood itself or the cabinets around it, rather the hood needs to be able to collect the "steam"(for lack of a better term) that is rising from the cooktop itself. In the horrible diagrams that will follow to show my point, steam does not rise straight up, as I'm sure you know, it expands outward as it rises. if you are doing stainless as the backsplash, it will be easier to keep clean as one piece than would tile with grout(although looks dictate this step. As far as the depth, the hood also NEEDS to come to the middle of the front burner...again for collection reasons! Here are the diagrams to show what I'm talking about...for my diagram, each _ will be equal to 6"; while the / represents rising "steam".
: ______ :: _______
\______/ : \______/
36" top w/ 36 hood 36" top w/ 42" hood

While it is obviously not to scale, you can see that the hood will collect more exhaust if it is oversised. Your designer should have already known this, and explained that rather than just telling you 'it needs gaps'. which is actually wrong. the way that cooking "splatter" actually comes to settle on cabinets and things is that as it rises it is heated and in vapor form. then as it cools, it reforms as a solid and settles with the help of gravity. So, if you have a hood with gaps, its going to stay dirty on top from this scientific principle alone. Not to mention the goofy look of a gap. I hope this helps in some way!

By the way, do you know what the two tone look on cabinets is called? By two tone, I mean when the lowers are stained and the uppers are painted/glazed? I can't seem to find anything on it.

Thanks for the feedbacks!! So if I go for the 42" hood, I'd make the stainless steel backsplash go the width of the hood, and have it hang on either side of the range 3" where it'll meet the other backsplash? Will it look weird at the cooktop? Its not a range, a cooktop on a cabinet with drawers under, (cabinets not in yet, so sorta in my head)
But my other problem is finding that 42" hood. Looks like the ones I like come in only 36" :
http://www.us-appliance.com/d3el36waho.html
http://www.us-appliance.com/rhfipa36rast.html
http://www.us-appliance.com/dkbo36slsiup.html
http://www.us-appliance.com/qdel36glands.html

We want to go with 400 or higher cfm, so maybe that'll help the collection even with 36"
Anyone seen similar looks in 42"?

Here is a link that might be useful: vent hood

Aaagh the hood dilema. This is the one part of the remodel that was the most confusing and frustrating. I wanted a slim, low profile hood too. But the thing is you need to check the CFM requirement on your stove. It should be with the spec or manual. 400 CFM probably isn't enough. We have a 36" DCS with a grill and we need 1200 CFM. And the size is important or the steam/grease will just go around your hood. (and give you that lovely yellow grease film.) Also, the mesh filters don't work nearly as well as the baffle filter - another important component. And the low profile slim hoods don't have anywhere to collect the grease/steam. If you want something less massive you could buy a liner and blower system and build a wood hood. Good Luck!

Honestly, it's a matter of personal preference but with a cooktop I wouldn't go with a stainless steel backsplash - I didn't even use one with my range. Continuing your regular backsplash behind the cooktop would be fine - unless you really want the look of the stainless steel backsplash.

We purchased a quilted stainless steel backsplash from Rigidized Metals on Ebay. We love it and the service was exceptional. They have several different looks in the stainless steel. They also come in different sizes and finishes. This is a 36" range with a 36" hood.

In case you noticed, those are pads under the legs of the range. We were trying to protect the travertine as we moved the range in and out for various reasons.
{{!gwi}}