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Fermentation Chest Freezer Setup

So I’m in the process of setting up a 7 cu-ft chest freezer for a fermentation chamber. I’m getting a couple brew haulers to make it much easier to insert/remove the carboys, a Ranco 2-stage digital controller, and a FermWrap (which I plan to tape to the inside of the freezer as opposed to wrapping around the carboy). I intend to secure the probe to the outside of the carboy under styrofoam to get an accurate a fermentation temp reading as I can from outside.

My questions are:

  1. anything I’m overlooking in this setup?

  2. what is a reasonable temperature differential to setup on the controller? 1 degree? 3 degrees?

I want to keep the temperature reasonably controlled but I don’t want to keep the 2 stages switching back and forth either.


IMO, 1 degree temp swing if measuring the beer temp. Example why: Temp wanted 65*. The beer raises to 66, freezer comes on. Air temp of freezer drops to (guess) 50* until the beer temp reaches 64*, then the freezer turns off. Until the beer temp reaches 65* again. In the mean time, the 50* ambient temp continues to cool the beer, possible down to 63*.

Also IMO, there is no need for a heater unless you are fermenting in a cold place. Unheated garage or super cold basement. Running both at the same time will surly cause one or the other to be working at any time.

If you are handy, I would save $40 and buy a controller similar to the one in my signature link.

there are differing opinions on how to locate the probe. !st opinion is to attach the probe to the fermenter which works fine but to control the temps all the fermenters would need to be the same volume b/c your attaching the probe to only one fermenter which accurately only controls that fermenter. any other fermenters temps if the volume is different will be either higher or lower than the controlled fermenter. there are cold and warmer spots in the freezer mainly in layers colder spots on the bottom and warmer higher up this is not an issue as long as you don’t stack fermenters. option 2 is to just hang the temp probe in the middle of the freezer to try and get a average freezer temp. and set the controller a couple degrees colder than intended ferm temp to account for the beer warming up during fermentation. Both ways work I can’t comment on option 1 since I use option 2 and set a 3 degree differential. This works fine for me with no variation in beer temp according to the strip thermometers on the fermenters. You definitely want to set a high enough differential temp so the freezer is not cycling constantly b/c constant cycling will shorten the freezers life.

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