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Easy Upgrade Series: Build a DIY Fermentation Chamber

Posted by on February 16, 2013

As I mentioned towards the end of 2012, I’ve got a few projects lined up and wanted to share these easy upgrades that all target producing higher quality beer at home.  We started off with a DIY stir plate for creating healthy yeast starters, then took a look at turning tap handles on a wood lathe (ok, that one was less about quality beer and more about good looking beer!), and now I want to look at an easy way to maintain your fermentation temperatures without breaking the bank.  Previously, I posted a fairly general post about the various methods of fermentation temperature control, but this week I want to look specifically at building a chamber that is large enough for 4 buckets/carboys or 6 cornie kegs that will efficiently heat and cool to maintain a steady temperature but not break the bank.

The most common (and more expensive) route is to purchase a chest freezer that is big enough to hold the amount of fermenting beer you need, add a wood coller if needed, and plug in a Johnson Controls temperature controller ($80-100) to override the built in thermostat and control when the freezer turns on/off.  This is guaranteed to cost you about $200 minimum, assuming you get a chest freezer used.  New, you’re looking at over $500.

So let’s see if there’s a better,  more affordable way.

Instead of having to purchase an insulated cooled box (read: a chest freezer) that can hold your beer, why not purchase a smaller cooling unit (read: mini fridge) and just extend it to the size you need by taking off the door and building a larger insulated box?  You can find decent used mini fridges on Craigslist for $50 or less fairly easily.  And I’m willing to bet that some of you have one laying around or know someone that has one laying around that they don’t use anymore that you could snag at little to no cost.  So let’s start with that.

Then there is the temperature controller.  The most popular models run $80+.  But it’s only a few components working together and packaged up in a plug-and-play box.  I’m no electrician, but it’s not a difficult thing to piece together yourself with a little know-how and some step-by-step instructions.  So let’s plan on building one ourselves for about $40 total (under half the cost of purchasing one).

Parts List


Temperature controller (total cost is $30-40)

  • STC-1000 temperature controller ($20-25) link
  • Standard duplex wall outlet ($1-3)  link
  • 3-prong extension cord capable of at least 10A…that’s almost all of them ($2-4) link
  • Project box, 6x4x2″ or 7x5x3″ ($6-8) link
  • Small cable clamp connector ($1) No link, but they’re dirt cheap in the electrical section at Lowe’s

Fermentation chamber (total cost is $40-60 + the cost of the mini fridge)

  • Mini Fridge ($0-50) …craigslist it.
  • 1-2 4×8′ sheets of 7/16″ OSB ($12-13 ea) link
  • 1-2 4×8′ sheets of 1″ thick foam sheathing ($12-13 ea) link
  • Two 2×2 furring strips ($1-2 ea) link
  • Two 2x4s ($2-3 ea) link
  • Hinges ($2-3 ea) link
  • Latches ($3-4 ea) link
  • Computer fan (salvage one from an old computer)
  • Power source for fan (use one of those old phone chargers you have taking up space in a drawer somewhere)
  • Heat source: either a regular 60W lightbulb (<$5) or a small space heater ($20-25) link

So, assuming you score a mini fridge for around $25, then your total cost for everything is just over $100 (try buying a chest freezer and a Johnson Controls temperature controller for less than that!)


Step by Step


Step 1: Order yourself one of the STC-1000 temperature controllers from Ebay.  They look like this:

This is an “STC-1000” and it will serve as the brains of your temperature controller.  It’s much cheaper than the Johnson models and they work really great.  It is available on ebay for roughly $20 shipped.  Downside is that they are in Celsius, but you can always tape a conversion table to the top of it if need be.  They ship from China and take a long time to get here, so order this first.

– Make sure it looks like the image above. There are 4 buttons on the front of it. There are other controllers out there that look almost identical but have only 2 buttons on them.  The two button ones aren’t any cheaper that the 4 button ones, and the 4 button ones definitely work, so just get the 4 button one.

– Read the listing for the controller carefully. There are a lot of sellers of these things on ebay, but not all of them sell 110V versions. Every seller sells 220V, but some of them have 110V versions as well. Most of the good sellers have the exact same listing information and you will almost certainly see this following bit of text in the listing:

NOTE: Unless required, we will ship the temperature controller with 220 V or 110 V versions based on the voltage of your countries. For example, if you are customers from United States, Canada, Mexico, Japan and Taiwan, we will ship 110 V versions. For customers from Europe, Australia, New Zealand, most Asian Countries, South America and Africa, we will ship 220 V versions.


If you don’t see this text, hen just assume that it is a 220V one. If you found one that looks like the image above, and it costs less than $20 (after shipping is added in), then it is probably a 220V one.

Step 2: Source a mini fridge

It’s best to get one that is tall enough to fit a carboy/bucket with an airlock (don’t worry if the freezer shelf blocks it) because then you can extend straight out instead of also having to extend up to make it tall enough.

Step 3: Build the base of the chamber

Start by building a base out of your 2x4s that is as wide as your fridge and long enough to hold the number of buckets and carboys that you want to fit, and the space you have available.

Add a cross beam in the middle for added support, as you will have a lot of weight on this thing.

Once the base is built, cut a piece of OSB to fit, then test fit your fridge on top of it.

Step 4: Add furring strips and insulate the bottom

Add furring strips across the base.  Your walls will screw into these and provide some support.  Once these are in place, cut and glue down 2 layers of foam sheathing.  The top layer will have to be notched out to fit over the furring strip.  Glue it all in place, but it should be a pretty snug fit.

Step 5: Construct the walls, door, and top of the chamber

Next, you will need to cut the OSB for the walls of the chamber, attaching another furring strip across the top edge and adding a sheet of foam sheathing to each side (You can also do 2 layers on the top, notched around the furring strip).

Make sure everything is well sealed (use calk and duct tape as necessary), and squared up (use clamps to hold it together while screwing and gluing).

On the side that will be facing out, cut a door in the OSB (but not the furring strip) and insulate it separately so that it will be able to swing open and shut.  Adding duct tape around the edges will help with this.  You can then attach the door using the hinges and latch to hold it shut.

The best order for everything is likely:

  1. Base
  2. Back wall
  3. Front wall w/ door
  4. End
  5. Top

Once it is all in place, go over it and make sure you’ve sealed all of the seams well.  DON’T seal it to the fridge quite yet, as you will want to slide the fridge out slightly when you run the wires for your temperature probe, fan, and heat source.  But once those are in place, then you should seal it all up to the fridge.

Step 6: Configuring the wall outlet recepticle

Looking at the outlet, locate the side that does *not* have the green ground wire screw is the hot side – this is the hot side.  Between the two screws on each side there is a metal tab.  By breaking it, it will allow us to power each outlet separately.  This will serve as the plug for our heat source and fridge, so we want them separated on the hot side only.

You do not need to break the one off on the side where the neutral screws are. Just break off the one that connects the 120V hot screws. Look at the back of the outlet to see which side is neutral and which is for hot voltage. To break it off, grab the tab with a pair of pliers and bend it back and forth until it snaps off.

Once this is done, you can cut a hole in your project box (I recommend the top or the back of the box) and attach the outlet.  Note that we will be attaching wires to the screws, so make sure you have room to get your hands around it wherever it’s mounted (or wait until after it’s wired to secure it in place)

Step 7: Wiring the temperature controller

Go ahead and cut the hole in the project box where the temperature controller will be placed.  Don’t bother securing it in place just yet, but we’ll need that hole to run the wires through.

Once that hole is cut, look at the wiring diagram on the back of the controller.  It shows you where to wire everything, but here is a nice easy diagram that you can follow as well:

The first thing to do is to create some wires by cutting off the female end of your extension cord.  Also cut off about a foot and you can repurpose those wires within the controller.

In written form, what you’re seeing in the above diagram is the power coming into the box from the extension cord. The hot line (black) from that cable needs to split and connect to 3 locations; pin 1 of the controller (to provide power to the controller itself), pin 5 of the controller (one side of the “switch” for heating), and pin 7 of the controller (one side of the “switch” for cooling). You can use a wire nut to connect all of those wires together.

The incoming neutral line (white) connects to one of the two neutral screws on the receptacle. Since you didn’t break off the tab between those two neutral screws, you can piggy back off the other screw and continue the neutral wire on to pin 2 of the controller to complete the power connections for the controller itself.

To finish the power connections to the receptacle, run a short wire from pin 6 of the controller to one of the receptacles hot screws. You now have a place to plug in a heater. Run another short wire from pin 8 of the controller to the other hot screw of the receptacle. You now have a place to plug in a fridge.

Incoming ground (green) connects to the ground screw on the receptacle and no where else.

The temperature probe wire connects to pins 3 and 4.

Use the cord clamp where all of your wire will be coming in/out of the box.  That would be your extension cord going in and the temperature probe wire coming out.  Clamp it down and secure everything in the box.

Step 8: Attach everything and test it out!

Now you have an outlet to plug in your heat source (light bulb or space heater) and an outlet to plug in your mini fridge.  For your computer fan, just wire it to the phone charger and plug that into the wall so it will run all the time.  Or, if your space heater has a fan and you only want the computer fan to come on when the fridge is cooling, then you can use an extension cord with a splitter plugged into the cold side of the controller so that you can plug in both the fan and the fridge.  The choice is yours.

Once you wire it all up, then you’ll want to calk and seal around the seams and where the wires are coming into the fridge (after you test to confirm that it’s working), and there you’ll have it, your brand new fermentation chamber for a fraction of the cost of most.

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59 Responses to Easy Upgrade Series: Build a DIY Fermentation Chamber

  1. Will

    I built something very similar about 2 years ago (yours looks nicer though), but my mini fridge could not keep up with the NC summer heat and it generated a lot of moisture. After fighting the July/August temps it kicked the bucket, so I ended up buying a massive chest freezer that’ll fit 5+ carboys. Have you thought about heating as well during the winter? Are you going to use a space heater or ferm-wraps? Cheers!

    • Chris

      Will – thanks for the complement!
      The moisture was likely due to poorly-sealed seams. If air is coming in/out, it will cause moisture build-up and cause the fridge to have to run more often. I have a bucket of damp-rid in it, as well as the computer fan to promote air movement. Additionally, I have calked and duct taped every seam, and added weather stripping around the door. This should avoid the moisture and help it keep up with the hot summers.

      It you look at the temp controller build, you can see that it accounts for both cooling and heating. I am using a small space heater, but you can also just use a 60w light bulb as well.

      I am not counting on being able to hold lagering temps during the summer, but I expect it will be able to easily hold normal 60-70 degree fermentation temps for a long time without turning on very often. But I will definitely let you know if that is not the case. Cheers!

  2. Josh

    What sized mini fridge should I be looking for 4.5cf or bigger?

    • Chris

      Really, the bigger the better. If you have one that is tall enough to fit a carboy with an airlock on inside, that will make it easier because the top of the ferm chamber can come straight out from the top of the fridge. You can get by with a smaller fridge, but you’ll have to add a little complexity to the build to make the box big enough.

  3. sharpstick

    I’ve installed two of these controllers for brewing and sous vide cooking. They work, but programming them is somewhat awkward. I made a C to F conversion chart and keep it and the instruction sheet with the unit.
    After a while the heating relay quit working and I splurged and got a digital Ranco unit. It has proved to be reliable and easy to use so far. (I think the other one is dead, too) I came home and found the fridge it was controlling off. Now I don’t trust these units.
    For enclosures, I like cigar boxes. Most cigar shops have piles of them lying around. I usually pay about $3 for a nice wood box. They’re fairly soft wood and easy to drill and cut.
    I’m planning to make a fermentation box like this next. I have an old crate that Italian tile came in that has room for 4 buckets. The guy I got it from had lined it with insulation and hinged the top. He had been putting ice in it but I am going to cut a hole in the side and slide in a tiny dorm fridge I already have.

    • Chris

      Thanks for the comment. I’ve not yet had any trouble with my temp controller, but it is definitely a bit tricky to program at first. I also know several folks who tape a C to F conversion chart on the top of their units.

      Cigar boxes are great. They also make awesome enclosures for a DIY stir plate.

      Good luck with the new fermentation chamber build, hopefully it works out for you!

  4. Rich

    I love your setup and am having a go myself. The problem is I don’t think we have the duplex type power outlets you use here in the UK. Do you know if there is a way to rig the temperature control box with 2 of these instead?

    I know the amps are wrong but I’ll check for a 15.

    Any clues how I can make this work here in England?


    • Chris

      Hi Rich – unfortunately, I am not an expert when it comes to different variations of this setup, especially using UK outlets/converters. All of my knowledge is based off of US electric power, so I don’t want to misguide you and take a guess, but I am sure that there are other good resources online that are specific to the UK.

      Good luck!

      • Rich

        Cheers Chris,
        I must have been reading your page upside down to begin with! I had a look again and realised how obvious it was that I just have to fit a normal UK duplex outlet. It wasn’t quite so easy as snapping off a bit of metal to get them out of parallel but I sorted it in the end. It’s working beautifully!


        • Chris

          Great! That is what I thought the case would be the case, but I didn’t want to lead you astray. Glad that it worked out for you.

        • Dave

          Hi Rich
          Can you show us how you wired your UK Duplex outlet?

    • Rick

      In the UK they use 220V outlets and their frigs are 220V also so he could build a 220 V system and use a UK outlet, frig, and controller with 220V systems. Their normal frig fits under the counter.

  5. Ty

    Did you put something over the insulation on the bottom so the fermentation buckets/carboys wouldn’t scrape it up?

    • Chris

      I had a spare piece of whiteboard that I used, but you could use anything. I’ve seen pegboard also work well.

  6. Stephen Lamade

    Hi. I’ve enjoyed the articles on your blog – particularly the one about the eHERMS. I plan to build this at some point in the future because I am getting started with decoction mashing and would like an easy way to maintain temperature in my direct fire mash tun without insulating and/or monitoring and constantly stirring. Currently I’m using gas to fire my tun and decoction pot, but I think it would be convenient to use gas to bring the mash up to temperature and then hold it using an eHERMS configuration.

    Re. the STC-1000: I have had great success with this using it with a chest freezer that I turned into a fermenter chamber. For colder months when the chamber is in the garage, I heat the chamber with a light bulb inside a large aluminium can. I can hold temps plus or minus 1 degree with this method.

    • Chris

      Thanks Stephen! Let me know how it goes. I love my HERMS system. I should post some new photos, as I have made some adjustments and built a better brew stand since moving into a house with a garage and some dedicated brewing space. The fermentation fridge is holding up quite nicely. Only thing in there now is a Sierra Nevada pale ale clone that we brewed for a class I was teaching. I use a small space heater for warmth, but I’ve heard of lots of folks using a light bulb and that working just fine as well. I like my chamber over a chest freezer because I don’t have to lift everything as high, and this fits my space better. But you can definitely achieve the same results with a chest freezer as the container. Cheers!

  7. Stephen Lamade

    One thing about a chest freezer is that you have to make sure that there is enough room on top for your carboys or Cornies, or whatever. I use 6,5 gallon carboys and there is only a couple of inches of free space above them. That’s no problem because I use a blow-off tube to a smaller container filled with Starsan/water – but’s it’s something to consider.

  8. Will Goeltz

    Did you use anything besides caulk / sealant and tape to keep the fridge from sliding out? For example,did you run a back brace furring strip around the fridge? Thanks for a great tutorial.

    • Chris

      Will – I did not. The fridge is in there fairly snug, and I built it basically in place and haven’t ever moved it, so I’m not too worried about it shifting. However, if you were going to move it, it wouldn’t be a bad idea to also include a back brace. Just remember that those fridges release a lot of heat through their sides, back, and top. so don’t cover up too much of it.

  9. Ian

    Actually laughed out loud (no I didn’t LOL) at “Downside is that they are in Celsius”. Whats the downside about using SI units? There are only 3 countries in the world that still don’t. Liberia, Myanmar and .. oh right…

    • Chris

      Nothing against celsius, but since this blog is directed towards brewers in North Carolina, it is worth noting, as most of our readers use fahrenheit. So if you are not used to calculating your fermentation temperatures in celsius, it is probably not ideal to have a thermostat that only reads in celsius – thus, that is a potential downside. But hey, if you prefer celsius, then it is definitely not a downside at all.

  10. Brandon Tate

    I’m assuming because of the disclaimer I should be getting the 110V temp controller?

    • Chris

      Make sure the description of the item explicitly says that it is 110v, or includes the text mentioned in the post. If they don’t specify, then it is likely the 220v.

  11. Dave

    I’m a little lost on the incoming green or neutral wire being routed to the duplex outlet. Where does this wire come from? I started with an extension cord… which only contains two wires. A positive and a negative.

  12. Dave

    Ok. Bear with me. I can not figure this bad English instructions for setting this controller. I want to set it to 22 degrees Celsius. Any help on walking me through it?

  13. Dan

    Thanks for posting. I have very limited space so I was going to attempt to make the chamber large enough to fit only 1 carboy. Given that will reduce the size of your original design, would you think it could get cool enough to double as a kegerator? I currently have a small Mini fridge that will require me to build up and out. Thanks

  14. Jamyn

    You can install custom firmware for the STC-1000 temperature controller that will use Farenheit, add brewing profiles, and more.

  15. William

    Hey man,

    Built something very similar to yours and I can only seem to get it down to about 52 degrees in the middle of an 83 degree summer. Have you had similar experiences with your fermentation chamber? I’ve triple checked to make sure everything is all sealed up air tight and I cannot find any noticeable leaks.

    • Chris

      Hi William – I use mine as a fermentation chamber and do not attempt to lager in it. Since it is extending the space that needs to be cooled, without a larger cooling element, it is going to struggle to get it much less than 20-degrees below the ambient temperature. I’ve not ever had much trouble getting it down into the low to mid 60s, but have not attempted to cool beyond that, as I have an indoor converted chest freezer that I use for lagering, chilling, and carbonating.

  16. Nick

    Thank you for putting out such a useful explanation of how to wire a temperature controller. I looked all over for anything that made sense, and your diagram and plain english wording was a life saver. I built mine today and it was a breeze thanks to you!

  17. Ken

    Chris, awesome write up and an all around great budget build. I just finished setting mine up and for some reason, the heating element seems to randomly turn on and refuse to turn off. I assume I’ve got a bad switch inside the controller. Cooling side works perfectly. Your thoughts?

    • Chris

      That does seem strange. I’d imagine there’s a bad connection somewhere in the controller, but without looking at it, it’s hard to say. Good luck!

  18. Justin S

    Chris, nice build! I am interested in putting one of these together. I have two concerns though. 1. Is there a way to set a few degree buffer between the heater and the cooler so that they are not fighting each other back and forth, (i.e. it gets too cold and then the heater kicks on and then too warm) 2. Where do you put the probe in relation to chamber?

    • Chris

      1. Yes, the thermostat allows you to set a buffer. I think it’s set to +/- 2 or 3 degrees by default.
      2. I usually tape the probe to the carboy. Use a rag or old sock for insullation on the outside of the probe, then tape it right to the carboy, and that’ll give you a pretty accurate read to the actual temperature of your beer.

  19. Tom

    What type of glue did you use? Was it some special construction adhesive or just gorilla glue or something?


    • Chris

      I don’t recall exactly. Probably just wood glue and/or gorilla glue.

    • Dan

      When I build mine I’ll be using wood glue or construction adhesive for wood to wood joints and silicone caulk for the foam insulation.

  20. Jason

    I’m picking this up on an iPad, but where is your heat source? I’m struggling with how to keep anything at 68 degrees or higher – currently putting hot water bottles in a decent Igloo cooler 3 times a day. (Would be the case in CO, Nor Cal, MI, MN) Ideally a small temp controlled heating element I could put in the cooler would work – haven’t found that element yet. My ambient temps are typically 60 at night and vary during the day – heat is a must – cool is probably not important. Any thoughts are appreciated!

    • Chris

      From the article: “Heat source: either a regular 60W lightbulb (<$5) or a small space heater ($20-25)” There is a link up there to the small space heater I use. It was about $20 when I got it, and it’s currently on sale for $15.

  21. John Toel

    I’m looking to build something similar right now. I bought a fridge on CraigsList last night for $20.00, 26″ tall x 18.5 ” wide, and I already have a Johnson Control from some past endeavors. I’m going to have this in my bedroom so I don’t believe I will be needing a heat source…. at least I am going to try to go without one. My apartment is always in the 70’s, and I only need to cool the box to the 60’s, maybe the 50’s at times.
    The other piece is I think I want to add more head space to the top, above the top of the fridge (and a door on top?) so there is enough room to accommodate a FastFerment in addition to carboys… Thoughts?

  22. Darrin

    What are your over all dimensions and what is your interior space? You say 4 buckets/car boys is this at s stagger or straight line? If so interior dimension is 48″ or so long

    • Chris

      At the size I built, it fits 4 buckets at a slight stagger. Counting the inside of the fridge, it’s probably 5-6 feet long. I just built it for the space I had available.

  23. Tim

    So would it not be less work and cost just to buy a small chest freezer and a Johnson Control?

    • Chris

      It would be less work, for sure. This build would be ideal if you already have a mini fridge you can use. Also, a mini fridge can usually be found for a fraction of the cost of a chest freezer. And building this thermostat costs a fraction of the cost of a Johnson Control. It’s more work and more time, but if you can get a good deal on the mini fridge, you can build this for about $100 total. The Johnson Control thermostat itself will run you $85+.

      I also like this build because you don’t have to lift the fermentors up into a chest freezer. You just pick them up about 3 inches and slide them into the chamber. Makes it a lot easier to move beer around.

  24. Keith

    Chris – do you have any issues with frost/ice build up in the freezer section of the mini-frig?

    • Chris

      Ice build-up is an indication that things are not sealed up well. Give it another round of caulk and make sure there aren’t any gaps. That should help fight the ice build-up. Otherwise, as with any mini-fridge, be sure to defrost it every once in a while, as most are not auto-defrosting.

  25. Keith

    Thank you Chris for the quick reply to my last post. Here’s another: in using the small 200 watt heating element, do you notice your beer temperature spiking above the set point? My concern is that the small heater puts out a lot more BTU than say a 60 watt bulb in a paint can; so, when the temp of the beer measured by the t/c on the side of the vessel triggers the controller to activate the heater, that the heater will run for some period of time until the measured temperature of the beer is at the set point before shut off, but because of the thermal inertia inside the enclosure due to the high BTU output will continue to raise the temp of the beer. Sorry for the awkward explanation, but I’m debating on whether to use a lower wattage heater (bulb in a can) that would more slowly add heat to the enclosure than the 200 watt heater you use.
    Thank you.

    • Chris

      I’ve not witnessed it, but it’s possible it happens. I usually put my carboys in there (it lives in the garage) and don’t really look at it much until I’m checking to see if it’s hit terminal gravity and is ready to transfer/dry hop/keg. I’d imagine it doesn’t swing too much, but you make a good point, and it’s certainly possible.

  26. Tom

    Hey there I am looking to start this project actually have to mini fridges and I want to use one of them for this project. I live in Florida so I’m not going to bother with the heating element but want to build a fermentation chamber for six carboys and keep the temperature around 65° for my sour beers. Would one standard mini fridge be strong enough for a space large enough for six carboys?

    • Chris

      You’ll definitely want a good fan in there to keep the air circulating, and you’ll have to make sure everything is sealed really well so you don’t lose any cooling power. And even then, I wouldn’t expect it to keep that size space more than 15-20 degrees below the ambient temperature, so on those really hot summer days, it may struggle a bit.

  27. Ryan G

    I know this article is a number of years old but I just wanted to say I’m in the planning stages of building one (wife kicked my beer stuff out of the house…) and this was a great read. I got some great ideas from it.

  28. Andy M

    Great post, thanks!

    I’ve built one very similar to yours, only mines on legs so I can transfer to keg without having to move anything first.

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