Hi,
Combustion air in/out should be external.
Exhaust is obvious, inlet not so, but noise while running and fumes on shutdown are factors in wanting external air.
Heating air is recirculated, so consider airflow through the space being heated.
I would have liked more separation of the two vents, but layout and locker space dictated they be on the same panel, about 300mm apart.
The heated air comes out with enough speed to avoid being immediately recirculated. (Unless someone huddles over it with arug over her knees)
Mount the pump where it won't resonate, use rubber sheeting or similar to isolate it acoustically.
If you need more leverage for $$ to spend, youcan drop the hint that it makes a dandy hair drier. (Just watch out for hair strands being drawn into the inlet and tangling up in the turbine)
Consider where the exhaust will run, I have melted various bits of clothing etc by not checking the locker for stuff moving before turning the heater on.
Cheers