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wrote:
Largely depends whether the wiring will take the additional load and
not suffer too much voltage drop. Manufacturers quite often use
thinnest cables possible to save copper=money, so with all design load
switched on there won't be any spare capacity for addl load. If the
cables are fat enough, there should not be a problem.
You need to find out the current total lighting load when all are
switched on, the extra load of the fans, the size of wire installed and
the length of the cable runs. Having done that you are in a position
to work out if it is really OK. The company will also argue that it is
unlikely that you will have everything switched on at the same time, so
it is OK. The breaker should still be sized to protect the cable - not
the size of the load.

If you replace the lighting on the same wire with LEDs you have spare
capacity for the fans, and wouldn't need to upgrade the breaker.

--
Kees