I have a chest freezer with a thermostat dial on the outside of the unit, so why do I need another temperature controller? What's wrong with taping and insulating a wired digital thermometer to the carboy and adjusting the temperature with the freezer thermostat based on the digital thermometer? I can't find any posts that address this. All I keep reading is that you need an external controller

1 Answer 1


The main reason you need an external temperature controller is because the thermostat on a fridge or freezer isn't in the right temperature range. Also they are typically not calibrated and offer only approximate control.

Some appliances have a digital thermostat, and you might be able to use these if they fall within the required temperature range. For example, I have a fridge that will go up to 9C/48F, which is fine for fermenting lagers. A diacetyl rest at 66F/17C is out of the temperature range, so I did that by moving the beer to a room at that temperature.

Having a temperature controller allows you to target any temperature range independently of the fridge thermostat.

  • Thanks. I was thinking that it had something to do with better precision alone. I hadn't considered that refrigerators max temp was so low. I was considering an Anchor Steam copy but fermentation is ideally at 60F with "California common" style yeast. I read in Ray Daniels' book that this style can be brewed with American ale but I was trying to be as close as possible to the intended ingredients. I've been practicing temperature control in a spare room by opening the window and letting it get colder in there to control primary fermentation.
    – thekolnik
    Dec 23, 2016 at 22:37

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