Ferm chamber temp

[Love_In_Da_Brew_Zone]

I have a chest freezer that is now converted to a fermentation chamber.....

I attatched the temp probe from the external controller to the side of a primary with 5 layers of insulation (silver reflective stuff that I believe is usually used to insulate hot water heaters) and have a heating source (light bulb) to keep the chamber up to temp and a small fan to circulate the air inside.

The air temp inside the chamber is staying right at 66-68 according to an independent thermometer in there, the probe from the controller is reading 66 but the stick on thermometer on the outside of the primary is reading 62 and will not climb much, even when I adjust the controller up to 75 and the air temp is about 75 as well.....

Which temp to listen to? Im confused.....dont want to overheat the poor yeast, but also dont want them to go to sleep and stop making the yummy stuff......

 

[LoCoBrewing]

I have a feeling your insulation is protecting your carboy from absorbing the ambient air temp. I would trust your probe that's taped to the carboy. Keep in mind it's warmer in the center of the carboy. Fermi wraps work great for this because it transfers the heat directly through contact. With your light bulb it has to heat the air then heat your wort which will take a while for 5 gals to warm up a couple ° with 75° ambient air.