It decreases the funtionality of the fan, so you comensate by going to a bigger duct or higher CFM motor.

It can be done just what Sophie says.

It does decrease the fan's function, but you can ask your HVAC folks to see if it is enough to worry about. Be careful about going to larger cfm fans, anything over 400 cfm requires make up air and it gets very expensive and can be a bear to accomplish.

What is the Btu level of the burners on the range? Is it a standard 30"? You will need to consider the length of the run but generally one turn isn't bad.

Most people will do fine with 400 CFM on a standard 30" average BTU range. If you do a lot of greasy, spicy or fishy foods you may find you need better than that. If you are putting in a 36" range or more you will certainly need 600 CFM or better.

Anything over 400 CFM does require make up air. In our area we have passed un-tempered make up air units by Best and Zephyr. These units are inexpensive ($200 or so) and fairly easy to install.

As always, I would suggest using a locally owned appliance store. Your appliance expert should be just that, an expert!