if you are being given a choice, have the humidistat mounted in the living space. There will be no adverse affect in regard to it's ability to control the humidity and will give you easier access to this control.
The contractor would probably 'prefer' to locate it on the return as this is easier than pulling low voltage to the finished part of the house. The system will operate the same regardless.

all the best, John.

 

Most like the return since you can get a pretty good avg reading for the whole house.

since you are going with an outdoor sensor on yours, you can set it and forget it. On manual model (no sensor) you need to adj when its colder out and bring it back up when it warms up.

Humidistat in the hallway can be fine if you have a return near by where it can get a reading for the house vs just what may be in the hallway.

 

humidity seeks its own level. In other words, if all the rooms are connected to one another and are part of the same central heating system, if you introduce humidity into one of those rooms, eventually the level of RH will level out the same throughout the space. Just as the thermostat is centrally located the humidistat when located in the conditioned or finished space is also. But, realistically, you could locate the humidistat anywhere in the conditioned space and it would work appropriately.

You choices are house or return. I choose house.

All the best, John.

 

Do yourself a favor - insist on a Honeywell 9000 IAQ - it will control your system, your ERV, your humidifier, your dehumidifier and has tons of user friendly features.

 

I agree with this also.

 

I choose DUCT mount.