So I'm just about to plug in my incubator except I need to plug in the fan.

My question is this - I have glass shelves in the incubator, but there is an inch gap between the back and the front of the shelves for airflow.

Should I put the fan on the bottom facing towards the back to blow the hot air upwards, or since heat rises should i put the fan on the top to blow the hot air back downwards?

Also, is glass an acceptable shelf medium, or should I switch the shelves to wire or something?