The basic purpose of a range hood started off as a way to reduce smells and control airflow over a cooktop. As time passed, range hoods were adapted to help control excess humidity created during the cooking process as well.
All range hoods, whether they be fans or microwave types, all come as recirculating form the manufacturer. Why? Because that's the most common installation a contractor will encounter in North America.
Homes built in the last 15 years are almost all vented to the exterior where as older homes are almost all recirculating type. Again, why? because older home are more breathable with reduced insulation and vapour barrier, lower efficiency windows and doors.
If you renovate an older home, you should certainly consider allowing the kitchen range hood to vent to the exterior. Once the home becomes better insulated and more air tight we want to remove that excess moisture from the home while cooking.
When I inspect an older home with a recirculating range hood I let the buyer know that it does not vent outside and offer suggestions as to how they could make that happen. I inform the buyer that this is discretionary for the most part and they may want to live in the home for a period of time to determine if it should be a priority for their family.
When I inspect a newer home the main thing I find with kitchen range hoods is that the fan hasn't been rotated to allow airflow to the outside. Microwave range hoods in particular require the installer to physically rotate the fan inside the microwave before it goes on the wall. This step is sometimes missed and although there is an exhaust pipe in the cabinet above, the range hood does not vent through it. To correct this the microwave is removed from the wall and the fan rotated, pretty simple improvement.
Over time I think that recirculating type range hoods will be in the minority as home efficiencies increase and managing moisture becomes even more important.
