These are exhaust ducts so you should be able to run them horizontally though the framing to the back face of the house unless the size of the range exhaust fan forces you to use a duct larger than the second floor framing depth.

Point source ventilation is an important part of an overall ventilation strategy for a home. Your mechanical contractor can help ensure the fans you select are appropriately sized for each application.

Best wishes for a successful project.

These are exhaust fans; ventilation involves the supply of fresh air.

The term "ventilation fan" or vent fan is commonly used in the industry to describe fans which exhaust air from bathrooms, laundry rooms, etc. Refer to Nutone's site for an example:

http://www.nutone.com/products/product-line/bath-and-ventilation-fans

Marketing departments of manufacturers often use technical terms inappropriately for their own purposes but in professional discussions we should use established industry definitions.

In the construction of buildings, "ventilation" is the intentional introduction of fresh air into a space whether by mechanical or natural means.

Fresh air that might enter a building through unplanned openings is considered to be "circumstantial infiltration" which has also been referred to as "adventitious ventilation" but that doesn't make an exhaust fan a ventilation fan.

You can take on the major manufacturers of ventilation--er, exhaust--fans if you want. As for me, I'll, well, go with the flow...

If you are ever responsible for meeting the building code requirement for ventilation or coordinating the design of the HVAC system for a house, you will find it advantageous to understand the difference between exhaust and ventilation. Until then, you can pretend the terms mean the same thing like Newtone does.

There are bathroom fans that contain a fan for exhaust and a fan for fresh air. This unit can accurately be called a bathroom ventilation fan. Because the supply and exhaust are balanced it can also act as an Energy Recovery Ventilator.

@JDS/Renovator8/Sanford W.,/the term "energy recovery ventilator" or ERV implies an enthalpic core as an integral part of the system. It is the enthalpic core-- which enables the transfer of both latent and sensible heat--not the balanced ventilation-- which qualifies a particular unit as an ERV.

I suggested that the OP consult with a mechanical contractor to assist with the selection and sizing of bath vent fans. I stand by that guidance.