There are many different ways to build your own fermentation room/chamber. Some are more complicated in design with multiple chambers kept at differing temperatures and others are simpler with only one temperature controlled fermentation chamber. Really what you need to figure out is a design that works with your space and budget. At the very least, you’ll need an insulated box, a method to cool said box, and temperature gauges to regulate/maintain your temps and voila! You’ve got yourself a fermentation chamber.
First decide how big of a project you want to tackle. Are you repurposing an old fridge? Or are you going to construct your own free standing fermentation chamber? Or maybe you have a spare room or old shed you’d like to repurpose? Depending on which route you want to take will determine what supplies you’ll need.
Personally I’m a fan of repurposing old appliances into new useful items. For instance, I built my kegerator out of an old fridge and saved myself a ton of time and money. Sure it doesn’t fit under my counter, but I can’t complain about the cool frothy brews that pour out the tap!
So let’s say you have a spare space, like a shed you’d like to repurpose or a spare room in your house. Really all you’ll need is insulation, a temperature sensor, an air conditioner, a sawzall, junction box and an extension cord. As far as construction tips/techniques, it all depends on the size of your space, and how technical you want to get. Are you looking to cover up that insulation with some nice wood paneling? Is the space large enough to warrant an overhead fan for circulation? Without knowing exactly what your working with, I can only give generalities at this point. But don't let that turn you off from tackling a DIY Fermentation Room. Built correctly with precision, this is your best bet for fine tuning your home brew fermenting.
Let’s say you want to repurpose an old fridge, or a chest freezer. Go onto Craigslist and you can usually find a chest freezer in pretty good condition for right around $100.00. Next go to amazon.com and pick up a STC-1000 thermostat for around $25.00. Next, head to Home Depot or Lowe’s and pick up a junction box and an extension cord. I've included a DIY junction box build in the links below. Overall setup and construction for this type of build is about as easy as it comes. Plus, you now have a chest freezer that you can use to store meats, fruits and vegetables in when you’re not fermenting!
Now if your available space and budget are bare-bones, I’ve come across a solution lovingly named the Son of Fermentation Chiller. These cost about $60 to make. A Son of Fermentation Chiller is essentially a fermentation chamber made of insulation panels which uses frozen water bottles instead of a cooling unit, a thermostat and a small computer fan that helps to circulate cool air and regulate the temperature of the fermenter. These are not the end all be all in fermentation options. They don’t really regulate the temperature so much as cool the chamber and circulate the cool air. Most are set so that when the temperature rises above a certain point, the fan kicks on to better circulate the cool air, but you must also check on your water bottle’s ice levels regularly.
For this style of fermenter, you'll need a bucket large enough to hold a carboy. I'd go with a 10 gallon plastic garbage can. Ice, a dark towel and a dark room. Place your carboy or bottles into the bucket and fill with ice. Next place your towel over the carboy with the edges of the towel contacting the ice. This will cause the towel to soak up some of the melting ice water and transfer it over the top of the carboy causing a 360 degree cooling chamber. This is easily the least technological and least precise route one can take, but it's better than nothing. Total price? $28.00
Below are links to some great DIY fermentation projects I’ve found around the web and even some wiring diagrams for your junction box and cooling system’s power supply. Honestly, if you have any aspirations of perfecting a recipe, a temperature controlled fermentation chamber is a huge step in the right direction.