This is our smaller incubator, it's a redbull true cooler.
It has 2 strips of 3 inch heat tape against the back wall running vertical.
A false wall placed about an inch and a half from the back wall.
A bathroom ceiling fan plugged into a rheostat to control airflow.
A smaller fan would work, but I love the ability to fine tune the airflow.
The fan sucks air from the top downwards over the tubs and pushes it through a hole in the bottom of the wall, over the heat tape and up to the top where it is blown out into the inc to repeat the cycle.
The probe for the herpstat is put through the top and it is hanging in front of the heat tape behind the wall, SUPER STABLE.
We did this same build with our larger incubator using 11x12 inch heat tape.
Ceiling fan, not recommended for any incs smaller than this one, they create heat ...
Top hole where heated air comes out, and where the thermostat probe is.
