Go with the 42".

4" wider. Technically for the btu's you'll be generating you need a larger hood. Make sure you do enough homework to size the CFM's of the hood to be able to handle the heat output of this size range. You can also consider building a hood and installing the "guts" such as Vent-a-hood system that will give you the lights and fan that you need.

The Vent-a-Hood option will work for a custom hood, it is the liner that can make or break the installation. Ideally the stainless liner of the now 38" hood is the same size as the hood, erg, custom sheet metal work in stainless....ouch. The Vent-a-Hood dual squirrel cage fan is rated to about 1100 CFM on high, so it is capable of venting most commercial style ranges. The one thing I'd like to know is, does your AGA, as I have heard, stay on all the time? What happens if it does? My understanding is that they developed the AGA Cooker for Great Britain as an alternate heat source. They need the heat for the cool days that are typical year round in England...is this range for the US market, where we really don't want or need that energy consumption and additional heat in the summer?

The model I have is different. It is six gas burners and four electric ovens. It is not the type that is used for home heating. After researching range hoods and looking at models rated from 900-1200 CFM I did find out that AGA does sell a range of hoods which are 600 CFM. I'm not keen on the look of them but I was surprised to see a lower CFM.

Really (obsessively!) thorough discussions on rangehoods over at Gardenweb, Christina.

Rule-of-thumb is to go a couple of inches wider than your range at least, and a more powerful exhaust system (cfm) at a low setting is less offensive (noisy) than a weaker exhaust at a high setting. I would think that you'd find 600 cfm for your size of Aga rather inadequate.

Thanks everyone!

You can build a hood to be like your cabinets, or do a shape covered in plaster/sheetrock, etc. Since you don' t have upper cabinets you can be very creative with your design - check thru Houzz for more ideas.

Also you can do a vent with a remote motor. It would be installed in the attic or on an exterior wall - check local codes. But that puts the noise away from the kitchen.

Option #1: since you don't have upper cabinets, you can go with an oversized hood, i.e. 48" is the next "standard" size up from 36". And no, it won't look "odd".

Option #2: get a hood insert and have your local craftsperson / contractor / builder manufacture a custom-sized hood for you - some examples attached below.

Also, it's not a matter of how much heat the range puts out; that's only 1 of the pollutants. A range hood takes care of multiple air-quality issues - airborne grease, carbon monoxide/dioxide, excess heat & steam, smoke particles, etc.

Here's an article on the multiple benefits of range hoods: http://www.futurofuturo.com/range-hood-benefits

This is a "range hood insert" - a fully-featured range hood, but built compact and without the finished outer shell.

It gets installed into a cabinet (or a custom enclosure), and works just like any other hood.

Not that this applies to your situation, but inserts also offer the benefit of completely concealing the ventilation among cabinets, for a smooth ultra-modern look:

Here's an example of an oversized hood - a 36" hood over a 24" cooktop.

Here's an even more extreme example. The hood is TWICE as wide as the cooktop. But the dimensions of the hood body echo the metal trim on the base cabinets, and the designer used the utensil rail to "echo" the width of the hood, which makes it look like it "belongs".

As you can see, you don't "have to" match the hood to the range. The hood can be larger, sometimes even 2X larger... as long as it looks good overall.

Thanks, Futuro Futuro! My project was completed in 2013 but I'll definitely forward your ideas to friends and colleagues who are also doing kitchen renovations.