South facing is the worst - overheats.
The RSPB: Advice: Siting a nestbox
Someone got one for my school - I made them take it back as you had to be watching the local screen at the right moment in order to see anything.
We now have one that only activates when there's movement, is accessed via a browser so it can be viewed from anywhere, and stores the data so you can wind back some days to see what's happened.
similar to RSPB Nest box cam
Costs more but it should deliver (no birds yet!)