38DD Mother of a Fermentation Chiller

In 1997 Ken Schwartz published plans for the Son of Fermenation Chiller, an ice & fan based chilling chamber for fermenting wort.

After building a Son of a Fermentation Chiller and using it for a while I found the following problems:
  • It would only hold one carboy
  • The analog thermostat sucked
  • It is a PIA to deal with the ice in deep narrow ice chambers
So I redesigned the controller first to use a digital remote sensing thermostat for under $25. Then I redesigned the Son of a Fermentation Chiller to hold two 7½ gallon carboys and two ½ gallon growlers for my blow off tubes.

This is the layout of the chiller with one side removed and the top and front removed.

From this top view you can see enough room for two carboys and two ice bottles

Cut sheet from a single piece of plywood foam:

Top closed:

Top open:

Front open:

The fan mounted in the right cooling chamber:

All three cooling chambers:

A tub full of ice in the central chamber:

Micah's version of the 38DD:

Awesome work, Micah!

All credit to the respective copyright holders.
- J Thornton
brant on 03/21/08 08:33 am writes
hey the link to the thermostat is dead.
Push Eject on 03/21/08 06:03 pm writes
Brant, you're right! It appears Thornton's entire site is gone.

I will contact him about hosting his sweet thermostat page here.

edit: Done!
Chad on 03/21/08 10:20 pm writes
Thanks! I was just composing an email asking about this. You rock!
Herb on 03/30/08 03:02 pm writes
Nice job but I have one question (so far). What size plywood? 3/4" ? or?
John Thornton on 03/30/08 05:12 pm writes
Hi Herb,

I used 1/4 plywood for laminating to the foam for the sides and top and I used some 5/8 ply for the base just because I had some on hand. Any size for the base from 1/2 up will be fine

John Thornton on 03/30/08 05:14 pm writes
Oh and I used some 1/2 plywood for the cooling chambers...

Herb on 03/31/08 08:11 pm writes
John, It appears from the pictures that the basic cambers from the diagram of the cuts on the plywood are surrounded by foam then inserted into another box.
Frank D on 04/21/08 11:08 am writes
Hi John,

Any chance you have the plans for how you cut the foam? If not no big deal..but if you did they would be nice. Great gadgets! Great Site! Keep it up!
John Thornton on 04/21/08 06:09 pm writes
Hi Guys,

The cut sheet is for the foam not the plywood. I cut and glued the foam together then skinned it with the 1/4" ply cut to fit as needed.


just scroll down to about the third picture

Push Eject on 04/21/08 06:29 pm writes
Frank, as to cutting foam there are a lot of options.

Craft stores have hot wire cutters (or you can make your own with a soldering gun), but I have found a big sharp chef's knife and a straight edge to work best!

toymaker on 04/22/08 10:25 pm writes
I made my own hotwire from a variable dc power supply hooked up to a .035 " piece of welding wire and a piece of 1/2" emt conduit bent into a U. I drilled two holes in the ends of the conduit. Then as insulators I used two ceramic wirenuts with the tips ground down till a tiny .036" hole appeared. then I fished the welding wire through the two wire nuts and twisted one end to anchor it the other end I used a small cable clamp. Then I hooked each lead of the power supply to each end of the wire. Next the power supply was turned on and dialed in to the correct voltage to generate the right heat. This will cut through the foam like a hot knife through butter.
My hot wire cutter is over 4 feet wide and will cut throug foam the entire length. So to cut through 2" polystyrene insulating foam (white blue or pink) which is 4' wide taakes about 2 seconds. the finished edge is better than the manufacturer's edge...
For more info google homemade hot wire foam cutters.
Rob on 04/30/08 10:46 pm writes

Where can I find the foam? I have been to my local Lowes and they have the blue stuff but it is only about 3/8" thick.


Push Eject on 04/30/08 11:13 pm writes
Rob, if you can find the white 2" extruded polystyrene you should be okay. Both my local Lowe's and Home Depot have it.
Surfbrewer on 05/15/08 12:09 am writes
Nice site, how low will the temp get in your chiller and how often do you have to change ice packs.

I like the modifications that you made to the design and the final product is actually pretty good looking. It looks like you were able to do the whole thing with one sheet of foam is that right? Do you recall what the total price tag was for the build? Thanks.

Baron Ken on 05/27/08 11:49 am writes
Where are you finding 7 1/2 gallon carboys? Most I've seen is 6 1/2 gallon.
John Thornton on 05/29/08 07:32 am writes
Surfbrewer, I built the whole thing with one sheet of foam. I had most of the wood laying about so all I had to buy was the foam and the trim. I don't recall the prices... and it would not be valid anymore with the rapidly changing pricing in materials...

Baron Ken, They are what is called acid carboys and they have a threaded top. These two were given to me and were found in a yard sale...

Beerinthe760 on 07/14/08 02:43 am writes
Hey John,

How low can you go with this? Is it possible to hit lagering temps? Wouldy post what the ambient temp was when you achieved your lowest temp? Also, have you used this going the other way to make the temp warmer during winter months? I like the idea (especially since it is cost effective).

Bluelou6 on 09/06/08 06:29 pm writes
Hey John,

nice build. I am going to attempt this weekend. I have 2 questions. What size fan did you use? What provides the structural integrity of the cabinet, the foam board or the plywood?


John Thornton on 09/07/08 07:07 am writes
Beerinthe760, You could hit lagering temps but not with ice. You can place a small light bulb or similar as a heater to warm it up.

Bluelou6, The fan I used was a 100mm but I don't think it matters much what size. Just so it blows the cold air up the tube. The foam will hold up on its own as in the SOF. The wood provides even more support and beauty.


ben on 04/14/09 06:48 am writes
I am looking to build this in the next few weeks, and so have a few questions. One, how long does the ice last? Two, does this actively maintain the desired/set temperature?
Crowds on 09/03/09 06:48 am writes
This looks great !
You say it can hit lagering temps but not with ice. What would you use instead if not ice ?

Goflyakite on 09/15/09 12:16 pm writes
How are others attaching the lower and upper door- I'm part way through the build- hadn't decided yet how to do the doors- I'm leaning towards dowling them for easy access straight on and off. Any ideas/input appreciated.

PS- the advice to use PL300 adhesive is appreciated (works great), I used white poly beadboard foam w/ foil on one side- looks nice (wouldn't recommend it- pia to cut and foam beads everywhere,) If I build another I'd use blue or pink closed cell board.
Tress on 10/26/09 07:40 am writes
Making clean cuts in 2" blue/pink foamboard (it is also called sheathing) is very difficult. If you do not have a hot wire or hot knife cutter, I would recommend (in order) an extended razor knife or a long serrated knife. I did not find out about the serrated knife's effectiveness until I already made a mess of a couple of the panels.
Rob on 12/07/09 09:43 am writes
Hey, is there any more descriptive plans available? The link to the original seems dead and I'm admittedly not super handy.
Scott on 01/29/10 06:41 am writes
What adhesive did you use to glue the foam board together and skin the plywood onto the foam?
John Thornton on 01/29/10 01:43 pm writes
Scott, I used yellow carpenters glue on the 38DD and it worked better than the high price glues I tried on the SOFC. You have to tape or pin things together so they don't slide around as the glue dries.

John Thornton on 01/29/10 01:45 pm writes
Rob, I'll have to fix the link...

unknown on 07/04/10 10:44 am writes
-- OK So I've cut my foam to exactly your cut sheet and I cant seem to figure how to put it together. The base seems to small at 19.5" x 24" (your specs). The rear is wider than the base yet your figure shows the rear sitting on TOP of the base. Can you please explain this to me or send me some better instructions.

Thank you sooooo much. Great work BTW!
John Thornton on 07/04/10 10:51 am writes
Mr. unkown,

The base is in two parts as shown on the plans. These must be edge glued together to form a 19 1/2 x 32 base.

Dave C on 08/29/10 09:57 pm writes
Used this basic concept to convert a shelving unit into my garage into a fermentation chamber, which will actually fit 3 carboys if I wanted it to.
I'm thinking of using the heating relay on the thermostat to trip a relay for a light bulb in one of the ice chambers for winter heating.
Any thoughts on that?
Adam on 10/21/10 09:32 am writes
Does the fan ever get wet from condensation? Thinking of trying this with an ac (instead of dc) fan and Johnson controller, but don't want to create a hazard with moisture and electricity...
Ken on 11/22/10 05:27 am writes
FWIW, I keep a cheapo electric carving knife for cutting closed cell foam. I ripped a slot in a long straight piece of oak flooring board on my table saw using a thin kerf blade and I use that to keep the blade square on thick material, say 2" foam where the knife tends to flex using an open guide. I have used the table saw with said thin kerf blade to cut sheets of foam as well...works great but do it outside or in the garage. Little pink bits go everywhere. Watch the kickback, you will mess up your styrofoam.
medical billing on 12/01/10 01:08 am writes
this post is very usefull thx!
Jeff on 09/11/11 03:25 pm writes
Hi John,

I had a question on the shelf that the carboys sit on. It looks like you've extended that into the foam on the sides. Did you take it clear out to the outside plywood on the sides and attach it to that?

At first I was thrown off by the measurements on the front foam pieces. I thought they were off by 1/2", but I see that the foam fits on each side of the shelf. I was just going to have my shelf/cooling chambers sit in place on the bottom foam. Will that provide enough support to hold two full carboys? I'm sure your design makes a stronger, and probably more air-tight shelf.

Thanks for sharing all your designs with us!
David in FL on 09/27/11 12:34 pm writes
Red alert on this project - learned after building a 6 gallon with an airlock on top will not fit. A 6.5 will have about .25 " clearance. If I was to build again I would making it 1-2" taller!
Jeff on 09/30/11 06:44 pm writes
David, I noticed the same thing. I'm in the process of building mine, and I'm planning to make the ice section roughly 6.5" tall instead of 8" so that my 6 gallon fits. The ice section will be too short for gallon milk jugs, but there should be plenty of other containers that will fit. You really can't change the actual dimensions of the overall chiller much if you're only using a 4'x8' sheet of foam.
David in FL on 10/02/11 08:04 am writes
Agreed I may modify mine - you can get a 6 to fit with blowoff as opposed to airlock.
Also anyone wondering why the hinged top as examples are shown without that it comes in handy for taking samples. Easier than sliding carboy out to sample.
http: ( remove space ) //i53.tinypic.com/vya1de.jpg
David in FL on 10/05/11 11:23 am writes

Just be aware if you alter your ice section you will need to alter both front facing sections. As for containers with lower clearance you can use the shoe-box size plastic storage bins $1 each at walmart.

Again though 6.5 G carboy with airlock or 6 G with blow-off tube may be your easiest solution. Great project but dimensions need to be adjusted based on common carboy sizes not obsolete ones.
Mark UK on 10/11/11 05:38 am writes
Hi John,

Any advice on how to hit lagering temp?

Mark G
Eric in Oh on 10/15/11 01:51 pm writes

Is there a blue print for the ice section, I have looked and looked but cannot seem to find one? Any help is most appreciated!

David in FL on 10/19/11 12:03 pm writes
Eric - you just need to make it so the front top section rests on it and the front bottom section slips into it. Basically the foam piece for the bottom is 8" so the opening of the ice section is also 8". Take into account the thickness of your plywood ( 1/2" for example ). The top piece that the carboys will rest on also juts out so the top front cover can rest on it. The bottom picture should illustrate that well.
TonyC on 10/21/11 01:26 pm writes
Thank you so much for the description and pictures, great job.

I have just finished my new 38DD, and was able to move my fermenting Lager (50 degrees) out of the "beer fridge". I made a few small changes to the design, but all in all it's a 38DD for sure.

- Casters
- CoolerGuys.com Fan and thermostat kit
- Tapered edges on foam to ease closing

Eric in OH on 10/29/11 03:39 pm writes
Thanks, I was trying to take the easy way out and have someone else do all that complicated (sacasam) math for me. Once I put pencil to paper I had a workable print in no time. Felt like I was back in mechanical drawing class! As a greenhorn to home brewing I am learning very quickly to figure out solutions to problems on my own when I am able. Forums are great but can keep you from using your brain in moments of laziness , ergo my post above. Thanks for taking the time to lay it out for me, much appreciated!
Mark in ME on 12/05/11 11:14 am writes
I'd die to have the Sketchup drawing of this. Any chance it's available somewhere?
Paul on 06/10/12 07:30 am writes
Very clever design. Thanks for all the information.
Did you have any idea it would generate so much interest?
ThatOneGuy on 06/14/12 08:03 am writes
Love the build! Working on it ASAP! Thanks!

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