not sure...but the less you microwave foods, the better off you are in my opinion. Plus a hood is what removes all the smoke etc from cooking out of your home, making the air a better quality. Go with the range hood.

We've been in our house eight years and are on our second microwave/hood combo. The only combos I've seen recirculate the air, as opposed to venting it to the outside. Here's my list of pros and cons, per my experience:

Hood-Mounted Microwaves: They do not last forever. They free up counter space. Their rounded edges make it less hurtful when you hit your head.
Hoods: They last forever. The corners can be softed with a loaf of bread and duct tape.

Next time, I'm going with a simple hood.

Not sure on the environmentally friendliness, but we have both, which were here when we bought the place. The hood is sorta built into the microwave. It's an Amana Radarange micorwave oven.

I generally avoid the microwave/range hood unless space is at a premium. Since it usually is in a kitchen, I'd take into consideration the following when making my decision.

From the sustainable point of view, it is more about the amount of electricity the hood or hood/microwave combo uses. Energy star appliances are the way to go.

Environmentally, the hood is great if it exhausts outside. If it recirculates, then it really isn't doing much for you. Assuming it vents outside, make sure it has a strong enough fan to properly exhaust your space.

Next, think about the life of the hood or hood/micro. The long it lasts you the more sustainable it will be, so see what kind of warranty is offered and check out comments online about product life.

If you're really serious, and why shouldn't you be? Then see what kind of environmental policies the candidates have and let that guide your decision.

Finally, go to a showroom where you can view your appliance out of the box. Is it easy to use? Is it easy to clean. Mine has little grooves that turn gross and require lots of cleaning. A mistake I won't make again.

Good luck.

I would just go with whatever you use more; i feel like the environmental ramifications would be hard to gauge... kind of apples and oranges.

i think the uses are very distinct though... either you are the type that likes to cook a lot and will find more use from a range hood, or you are the type that microwaves food a lot and doesn't cook as often.

btw... those microwave vents always stink.

Ditch the microwave and get a hood.

We installed a restaurant hood in our kitchen - we cook a lot - and have loved it ever since. Searing, baking, roasting, frying, it's all possible without the rest of the house smelling.