Question: There is already a [general question about ways to control fermentation temperature](https://homebrew.stackexchange.com/questions/861/temperature-control-for-fermentation). This question, however, is more specific - it pertains to active fermentation temperature control using refrigeration. And I'm making it a community wiki.

In a nutshell, I want to know which type of cooling system I should choose, and why. So I will list the various options and if you have used any of them, I ask that you please edit the answer with the pros and cons.

Answer: 
There are quite a few choices in refrigeration for building a fermentation chamber. What are the pros and cons of each option? Assume that whichever is chosen, it will be controlled by an after-market temperature controller, allowing for precise adjustment of fermentation temperature.

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### Upright Refrigerator - Freezer on Top

Pros:

* Very easy to find on [CL](http://craigslist.org) and the like.

Cons:

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### Upright Refrigerator - Freezer on Bottom

Pros:

Cons:

* Being fairly new to the market, these types of fridges are generally more expensive than freezer on top versions.
* Requires lifting up and in of carboy of beer. Becomes a bigger challenge with greater than 5 gallon fermentors.

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### Upright Refrigerator - Side-By-Side

Pros:

* The dividing wall can be removed, allowing for the creation of a large chamber than can hold multiple fermenters if you build a sturdy shelf mid-way up.

Cons:

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### Upright Refrigerator - French Door

Pros:

Cons:

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### Upright Refrigerator - Freezerless

Pros:

Cons:

* Difficult to find used.

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### Upright Freezer

Pros:

* Very easy to find on [CL](http://craigslist.org) and the like.

Cons:

* Not meant for temps above freezing, so they don't have active humidity control. Mildew can be a problem if steps aren't taken to dehumidify.
* Some have the refrigerant lines built into or under the shelves. If so, moving them to make room for your fermenters can be difficult without kinking the lines (and thus ruining the unit).

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### Chest Freezer

Pros:

* Very easy to find on [CL](http://craigslist.org) and the like.

Cons:

* Not meant for temps above freezing, so they don't have active humidity control. Mildew can be a problem if steps aren't taken to dehumidify.

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### Mini (Dormatory) Fridge

Pros:

* Easy to find for cheap or free

Cons:

* Can only hold one carboy, many can't even hold that
* In many, the freezer shelf contains the refrigerant lines. Moving this out of the way can be difficult or impossible without kinking the lines and thus ruining the unit.

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### DIY Fermentation Chamber

Imagine a wooden frame, well insulated with extruded polystyrene, cooled by a mini-fridge.

Pros:

* Can be build to any dimensions

Cons:

* Moderate DIY skills required
[Mother of Fermentation Chamber](http://www.yeastbound.com/brewhouse-equipment/36dd-mother-of-fermentation-chiller/) and [Son of Fermentation Chiller](http://www.olderascal.com/brewing/fermentationchiller/index.html), are both DIY but use containers of ice & a fan instead of a fridge.

You can also [use thermoelectric cooling (TEC)](http://forum.northernbrewer.com/viewtopic.php?f=1&t=72229) instead of ice. A little trickier to set up, but easier than hauling around bottles full of ice.

Of course, a fermentation chamber might need to both heat and cool, depending on your climate. If I brew a big beer in the winter, I need to cool it during the first day of active fermentation but after that I need to keep it warm. For that, you might want a [two-stage temp controller](http://morebeer.com/view_product/16664/102282/Ranco_Digital_Two-Stage_Temperature_Controller_-_Wired), with one plug powering your cooling system and one powering your [heater](http://www.northernbrewer.com/brewing/marketing-categories/landing2/electric-fermentation-heater.html).