Here is what I did for my Apex 42. I suppose begreen could be correct about cooling the firebox, but my impression is the fan is not significantly impacting the firebox temp. I picked up a manual switch that allows me to run it "manual on" mode or "auto on/off" mode. I mounted it in the lower grill using a factory gap in the face (no drilling required). Please note: I'm not a professional electrician; if you go this route, please do your own research and/or consult a professional.
Details:
My problem is the fireplace take a long time to decide it is hot enough to turn on the fan (and there is no manual override). The basic issue seems to be the thermostat sensor is on the bottom right corner and things like ashes, etc. can make it so that the thermostat does not kick in for a long time (can take over 30 min with the stove at 600 degrees according to the little read out).
Based on this, I wanted to be able to over ride the default, but I really like that it will automatically turn the fan off after I go to bed and the stove cools down.
So, I picked up a toggle switch with 2 "on" settings that handles 2 circuits per side:
View attachment 304078
As you probably already know, the 2 center tabs are the "out" terminals (no matter which setting the toggle is set to). The 2 tabs on the left are "in" and will be connected to the center tabs when the toggle is positioned left. The 2 tabs on the right get connected to the center tabs when the toggle is positioned right.
So, this allows me to have 2 separate circuits entirely. I'm sure I don't need this, but it keeps it clean in my mind.
There is easy access to the two wires that hook to the sensor. This is how I hooked up the switch (the left "down" arrow is the hot lead, and the right "up" arrow respresents the neutral/ground side):
View attachment 304080
In "manual" mode, I bypass the temp gauge entirely (it should be totally isolated from power). In "auto" mode, the "in" and "out" wires to the temp gauge are hooked up like before.
This setup has been working for the past 2 years or so.