The watts is what cooks inside. The CFM is the strength of the exhaust fan. (Most GardenWebbers will not recommend an over-the-range microwave.)

As Debbi mentioned. Watts mentioned is for the cooking power of the microwave and has nothing to do with the CFM of the fan..

400 CFM if it is exhausted to the outside will work for most cooking but the capture area of an OTR microwave is very small. Only 12 -14 inches deep.

In comparison a 300CFM hood that is 20-24 inches deep will perform better than the OTR due to a larger capture area even though it is 25% less in CFM.

Neither.

(ETA -- as I was posting, I see that Debbi and Jakvis were also posting. Here's my 2 cents, anyway).

The "watts" number represents the power the microwave part uses for cooking food inside the oven. An 1100 watt MW will cook a bit faster than a 1000 watt model. It has nothing to do with the capacity of the vent fan.

An "amps" rating tells you what kind of plug and circuit you can plug the whole unit into. Almost all MWs and OTR/MWs run on standard 120v wall outlets. Any 1000 or 1100 watts OTR/MW will run on a regular 15 Amp 120v circuit. (OTR = "over the range"). (There are a few OTR microwave speed ovens that are designed to run on 240v circuits, such as the 240v versions of the Advantiums, and their amperage needs will be different.) Again, this has nothing to do with the vent fan.

The strength of an exhaust fan is reported in CFM -- that is "cubic feet per minute" which represents how many cubic feet of air the fan can (theoretically) move through the vent in a per minute.

It has been awhile since I looked at OTRs for a friend, but I do not recall any models with more than 400 CFM exhaust fan capacity. Maybe somebody here has seen a newer one?

None of the above (referring to the OP's question, and not the comments generated while I was dawdling). The rated power of a microwave oven is usually that supplied to the magnetron generating the microwave energy. An 1100W microwave oven will boil a cup of water about 10% faster than a 1000W microwave oven. Actual microwave energy emitted is reportedly only 65% of the magnetron's input power. The fan uses much less power than the magnetron. Total power draw of the appliance is higher and usually specified on some name and data plate or painted-on message.

The specified fan CFM (air flow rate) is either that of the fan alone hanging in the air, or that of the fan in place, without any other ducts or replacement air restrictions. So if the microwave oven is hooked up to a duct, the actual flow rate is likely to not be more than 300 CFM and possibly less.

I've never had the impression that microwave oven manufacturers were providing more than minimal ventilation, as this is not usually their main selling point. Further, they usually don't have room for significant fan blade sizes. Someone else here may be able to direct you to a higher flow rate microwave oven if it exists.

You can duct the air outside and use a secondary external blower to help move air if you want better removal. However, these devices will not perform smoke capture and containment as well as a proper hood.

A better name perhaps to match their usual performance is Over the Toaster Oven microwave.

kas

Thanks to everyone for your replys

"I want a microwave that pulls a lot of smoke out"

I'll just emphasize what has been said above. If you want to pull a lot of smoke out, an OTR MW is just not going to do it. The couple little squares on the bottom of the MW for the exhaust are inadequate for coverage over the burners, and won't pull much of anything. The 300 or 400 cfms advertised for OTR MWs are just not real. Idk how the manufacturers get away with saying that.

If you want to pull smoke out, get a proper hood. Also, make sure your exhaust duct to take the smoke out of the house is large enough - best would be an 8" diameter duct.