the latter. buy a 42" hood liner. Here is a link that might be useful: here's one

One thing you should keep in mind when you shopping around for a range hood to go over a 48â stove, is the size of the hood. Many (almost all) American-type brands are made with good quality but are pretty oversized and bulky. Even though itâÂÂs a âÂÂcommercialâ look, which may complement a traditional kitchen design, it will block much of the view, which is especially important if your kitchen is shared with the living room or has a view of the outside. On the other hand, European-type range hoods, even though they usually have the same suction power, are typically much more slim and âÂÂlighterâÂÂ, and would complement a modern or contemporary kitchen very well. I think your decision has to be based not on somebody elseâÂÂs advice, but on your own considerations of your kitchen design and personal taste. Some people like great big bulky commercial-style hoods, some people like slim and futuristic. In your case, the overall look doesnâÂÂt make any difference, since itâÂÂs going to be hidden inside the cabinet (whatever the reason is) - as long as the quality of the product is good.

It's a universal recommendation that the hood be at least 6" wider than the surface it covers. And as deep as you can manage. It has nothing to do with the fuel used to heat the food. It has to do with the fact that smoke, steam, smells, and aerosolized grease particles rise upwards and outwards. That's physics. A smaller hood can't capture all of those yucks. Stronger fans can't compensate for a lack of capture area either. It's more important to have a good capture area than a strong fan.

You need a 10" duct and plan on higher CFM either mounted inline or external to keep the noise down. A higher CFM hood at lower speed will suck better and be less noisy. Even if you don't make smoke and fry all the time, using the hood will be more pleasant if it does it's job without wailing like a banshee. Baffles are way better for keeping it easy to clean. Look for Rangecraft hoods, Independent hoods or Tradewind. Modernaire custom hoods are an option if you want the look and the $$ works. Fantech, abakka, etc. make inline or external hood fans. I personally do not like VAH's squirrel cage design. Here is a link that might be useful: Great thread on ventilation