

Since the summer I have been putting together and upgrading a fermentation fridge one piece at a time. The fridge (pictured above) can hold two 6.5 gallon carboys and can maintain a steady temperature year round. It has a range between 35°F and 80+ °F. This is a quick overview of the setup.
I keep the fridge in the garage where temperatures fluctuate drastically throughout the day. In the summer the fridge and digital thermostat alone worked to maintain fermentation temps at about 50°F for lagers and 68°F for ales. Once the cold fall and winter weather hit, I needed a way to keep it warm inside. I solved that problem by putting a waterbed heater in the bottom of the fridge on the second stage of the temperature controller. Later I added a fan to solve the problem of uneven heating that the waterbed heater causes. Without the fan, the bottoms of the carboys can get quite warmer than other parts.
The equipment I used consists of:
I drilled a hole in the side of the fridge to run the wiring for the heater, fan, and temperature sensor probe through. I also drilled holes through the horizontal barrier that divides the top freezer from the lower fridge to allow the cold air from the freezer to sink into the fridge for more efficient cooling as well as colder possible temperatures in the fridge portion.
I managed to find a prewired Ranco temperature control unit, which I recommend unless you have any experience with electrical wiring. The unit has two plugs to which your heating/cooling devices connect for power, and will power each one on/off in accordance with the temperatures you program it to maintain. I attach the temperature sensor directly to the outside of the carboy inside using a piece of electrical tape.
The Ranco temp control unit is the costliest portion of this endeavor. However the warm fuzzy feeling you will get every time the digital display tells you the exact temperature of your fermenting brews is well worth it over time. Furthermore fermentation temperature control will greatly improve the beer you brew.
One word of advise I can offer on the use of the dual stage controller is to make sure you allow a 1 degree buffer between the two stage temperatures (i.e. cooling circuit at 69°F, heating circuit at 67°F) with a 1 degree differential. If you do not allow an appropriate buffer between the circuits, the heating and cooling circuits can rapidly cut on and off trying to cool and then warm repeatedly. With the one degree buffer, the temp should eventually rest on the buffer temp and the heating and cooling circuits will activate as needed.
Some people use chest freezers as fermentation chambers. However, I believe that upright refrigerators like mine are more well endowed for this purpose if you are just fermenting a couple beers at a time. First off, it is very difficult to lift a filled 6.5 gallon carboy in and out of a chest freezer. Second of all, a chest freezer does not allow as good of a view of the action as an upright refrigerator. Just open the door and quickly see how fermentation is progressing.
Despite several recent nights in which outside temps plunged into the 30's the fridge has been maintaining a steady 68°F. Pictured in the fridge now is an IPA I brewed this weekend.