An Idiots Guide to Temperature Controllers

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Up until now you’ve been fermenting your beer in the basement, or in that hall closet that stays nice and cool. What if you want to brew a saison that calls for higher fermentation temperature, want to try your hand at lagering, or even dial in your standard ale fermentations more precisely? You need a way to control the fermentation temperature.
Temperature control isn’t just for beers that ferment higher or lower than average. All of your batches can benefit from being at the right temperature at the right time.
Homebrewers used to have to come up with clever ways to keep fermentation temperatures in check. Take the “Swamp Cooler” method, where a fermenter is placed in a vessel of ice water and a T-Shirt is draped over it. The theory goes like this: The T-shirt draws up water, which evaporates and keeps the fermenting beer 10-15 degrees cooler than the ambient room temperature. That’s a great way to keep fermenters cool on a budget, but with a little investment, accurate, and constant temperature control is easy to achieve.
When it comes to temperature controllers, as with most aspects of homebrewing, there’s no single way to do it. And these days, it’s easier than ever to build (or buy) a temperature controller. Here’s what you need to know if you’re taking the plunge into homebrew temperature control.
My Temperature controller

Single Stage vs. Dual Stage

There are two main types of temperature controllers: Single Stage and Dual Stage.
Single Stage temperature controllers can only control one output (heat or cold) at a time. If your only concern is keeping your fermenting beer cool in the summer, or you just need to keep your kegerator at a constant temperature this might be the way to go. Single-stage controllers also work great for lagering.
Single-stage controllers aren’t great for keeping a constant temperature during ale fermentation. Let’s say you’re fermenting in your 55-degree basement, using a single-stage controller hooked up to a heating element. With the temperature is set at 64 degrees, you’re guaranteed to never go below that. But what happens if the fermentation is active and the temperature starts rising naturally? You can try and monitor the temperature and switch from heat to cool manually, but that’s a pain. Dual-stage controllers can solve this problem.
Dual Stage temperature controllers control both hot and cold outputs at the same time. In the example above, using a dual-stage controller, the cooler would kick in once the temperature reached the threshold, keeping your fermentation chamber at the correct temperature.

Digital vs. Analog

Mounted digital temperature controller
Digital controllers allow you much more precision as you can set the temperature and other variables such as temperature differential. Digital controllers have a digital display. Analog controllers are less precise and usually feature a knob to change the temperature, and not much else.

Temperature Probe Placement

Every temperature controller uses a temperature probe. There’s some debate on how to get the most accurate reading, but two approaches seem to stand out.
If you want to measure the temperature of a liquid, it makes sense to insert the probe into the liquid. This is the idea behind thermowells. For about $25, you can get a stopper that has an opening with a tube that extends down into the fermenter. The temperature probe is inserted into the tube. There is also a hood model.
If your temperature probe is too big to fit into the thermowell, or you’re saving your cash, another option is to tape the temperature probe to the side of the fermenter and then insulate the three sides not touching the glass with foam or bubble wrap.
Finally, some people suggest placing the temperature probe in a jar of water inside the chamber.

Cooling Your Fermenter

A chest freezer or mini fridge is usually used to control the cooling. If you’re going with a mini fridge, look for one that has a single door, removable shelves, no freezer compartment, or has a freezer compartment that you can easily fold down. You may also have to remove the door shelves in order to fit your fermenter inside.
If you’re going the chest freezer route, check out this forum thread on different models.
If you’re buying either a chest freezer or mini fridge second hand, ask the seller to plug it in the night before, so you know it works when you get there.

Warming Your Fermenter

Since you’ve already got the fermentation chamber, warming your fermenter is fairly simple. Commercial products such as the Brew Belt or FermWrap wrap around the carboy or bucket and provide a source of heat. They run about $30. Of course, there’s a DIY way as well. A paint can heater is just what it sounds like. To make it, you wire up an incandescent light bulb inside an empty paint can. Place the heater in your chamber, and when the bulb turns on, the heat warms up your chamber.

DIY vs. Store-Bought

This is probably the biggest question to ask when you’re shopping for a temperature controller. A store-bought dual-stage controller like this Ranco will run you $150. On the other hand, you can build the same thing using an STC-1000 for way less than half the price. It comes down to convenience (and price) vs. saving money, but spending more time building something.

Temperature Controllers:

Here are some commonly used temperature controllers:
Chart of most used temperature controllers for homebrewing.


The NTC thermistors that the cheap units use are waterproof. Wash, sanitize and stick the wire right into the carboy via the blow off or airlock hole in the stopper. If it gets to the point where you think it can no longer be sanitized, replacement probe thermistors are <$5 from eBay and other similar sources. You don&#039;t actually need a thermowell.
I use the STC-1000 in my fermentation chamber setup. For heating, I use a ceramic heating lamp made for reptile enclosures. No light, no paint can, and I'm sure it will last forever! I also have a 120VAC fan blowing right over it to distribute the heat. Works GREAT!
Also, highly suggest if you don't stick the probe into the beer, at least tape the probe to the outside of whichever carboy is actively fermenting. The temp of the beer and the air surrounding can vary by >10*F, especially with big beers. Not good to let it get that hot unless you're going for a saison of course. ;)
Paint can heaters needs to stop, as does space heaters.
Use a low wattage, low heat density heater and preferrably a properly sized fuse and some overheating protection.
Down here in South Texas, it can be hot one day and below freezing the next. So, in the winter, I use the paint can heater in my freezer and it's turned on all time...if it gets too warm, the freezer is plugged into to the controller and it will kick on and cool back down....single stage can work. Uses a bit more electricity...like pennies per day...I can run it like this a long time before I could break even on a more expensive dual system controller.
IMO, temp control and building my water up from RO have produced the most noticeable improvements in my beers.
Eh cheapest controller on there does dual stage. Not too bad to hook up either. Forcing your fridge to fight heater output sounds horrible.
Good article! I have used the STC-1000 for many years but now only use the Raspberry Pi running the BrewPi software. This device is excellent at maintaining temperatures by making very small changes in the temperature of your fermentation chamber. I use a reptile element in a light socket for heat and the freezer (fermentation chamber) does the cooling. If you want consistent repeatable fermentation temps and don't mind spending a few bucks to get this set up, the Raspberry Pi running BrewPi is for you! There is a small learning curve and will require some DIY skills but, it isn't too bad. I found the howto on HBT.
The Brewpi spark is neat and does require some decent "geek cred"... However if you have even a small amount of "geek cred" home brewers should also consider the DIY version of the brewpi that is popular on the forums of this site. You can make a bad-ass brewpi system for between $60 to $100 depending on your tolerance for waiting for parts from China and what you house it in.
See the thread here - https://www.homebrewtalk.com/showthread.php?t=466106
I used a duel stage ITC-1000 that can give you ( C or F ) readings. Get the 110vac unit (15 to 20 on Ebay) The higher price is available in US and the cheaper price is from China and takes 3 to 4 weeks to get. It cost me under $18 to make with a old plastic box I had. The hardest part is getting and cutting out the holes in the box. A plastic box can be had at the hardware store in the electrical section. (Apx $11) There are also YouTube videos that show you how to build it using a STC-1000. Check out thrift stores, yard sales for a box to build in. You just need room for a AC Duplex socket and a controller. I built 3 of these and gave a demo at our beer club meeting on how easy it was to make one. Had lots of interest there.
The best dual-stage temp controller on the market is glaringly absent:
"alphaomega on May 18th, 2016 - 3:41pm
Paint can heaters needs to stop, as does space heaters.
Use a low wattage, low heat density heater and preferrably a properly sized fuse and some overheating protection."
Why do paint can heaters need to stop? What low wattage, low heat density heaters do you suggest?
Yeah, I had trouble cutting the holes in my box, too. A Dremel or similar tool would have made the process easier! I drilled holes in each corner and then used a fine-tooth blade on the jigsaw.
I'm not horribly against the paint can heater...but I use a ceramic reptile heat lamp. 100W. Not that high of wattage, and I just blow a fan over it to distribute the heat throughout the fridge. Not very expensive at all. Just seems easier, cleaner, and more efficient to me
Im considering getting the Inkbird itc-308 but theres one thing I read online which I dont like the sound of...
"When your temps get out of range the unit just sounds an alarm and shuts off. You have to adjust the temp parameters again in order to raise or lower the temperature to the range you are needing"
Does this mean if it gets too high or low an alarm will sound and will then shut down leaving the temperature uncontrolled, If im out of the house and this happens the fermentation temp could get too high and what was the point in the first place? I cant find any info about this has anyone got any experience with this.
Would the temp only go out of range if there was some sort of failure of the heating or cooling
Any info be great
The 'plans' circulating around are badly designed (heat rising into the socket and no ventilation). You don't need a lot of heat, since it is in an enclosed, insulated space, and slow temperature changes really are preferred anyway.
Basically, avoid anything that would get too hot to touch. Heating cable/brew belt, reptile heating mats or the british 'tubular heater' would be good choices.
Heating cable can be 'woven' into an oven rack or a fridge wire shelf or something similar if you don't want to attach it to the fermenter.
Also, sufficent distance between the heater and the interior of the fridge, a properly sized fuse and if possible some over heating protection (thermal fuse), would also be good ideas.
The STC-1000 is so ridiculously easy to wire with the proper diagram. Really not sure why anyone with even the slightest DIY abilities wouldn't go this route. Checkout this step-by-step build guide.
I use the Inkbird ITC-308 with my keggerator. Super simple to hook up and works well. No need to take apart or soldier anything makes it a winner in my book! Oh yeah and its CHEAP on amazon with prime.
I use a duel stage ITC-1000 from ebay for about $16, the box and dual plug and wire were all part of my clutter in the garage. A reptile heater that screws into the light bulb socket in my fermenter box doesn't seem like it wants to get warm, so I use a 40 watt light bulb wrapped in alum. foil. Keeping it cool in the summer is a little tricky, I use ice in buckets in the summer - my fridge in the beer shack always has an ice bucket at the ready for me. All in all, I recommend the $33 ready built temp controller you can find on ebay altho building the ITC-1000 box was a lot of fun.
You have left out a number of other options though.
The BrewTroller can do this with as much nerd cred as the BrewPi and a LOT more possible function. There is also the BCS, the Hosehead, and the Strangebrew setups. Multiple zones with heat/cool are possible, and even temperature schedules and more!
Note the Black Box uses a programmable version of the STC-1000 flashed with the firmware alphaomega developed and freely distributes. Anyone wanting to build their own as an alternative, and use this excellent firmware upgrade, needs to ensure they purchase the correct STC-1000. Details are available here https://github.com/matsstaff/stc1000p.
This was not my experience with the inkbird, it alarmed when I initially added my cooled wort which was above the high alarm threshhold, I jabbed a button to silence the alarm and it continued to cool.
I'm not sure that is accurate, when fermenting we are concerned about the beer's temp during fermentation not the ambient surrounding air. This is why you would have a thermawell in place optimally to monitor the fermentation temperature and adjust as needed. Example my IPA might want to ferment at 64, but in order to keep it at 64 my chamber may have to maintain a temp of 60 on avg due to the thermal dynamics of the fermentation. If i were to set my ambient at 64, I've seen beer temps closer to 68-70 which is much to warm. Just my .02
TheMuffinMan suggested to tape the probe to the side of the fementor. That won't be ambient air. Experiments have been done showing the temp on the side of the fermentor is just as accurate as a thermowell if insulated well.
I can agree with insulating it well, I just never had the accuracy of simply taping it with out some bubble wrap etc. Just saying a thermowell works nicely if you don't mind spending 15$. I just got tired of having to tape something up. By all means if you have a system that works it's golden and don't change it. cheers!
Of course this overview mentions a few popular choices, but I use an ALVA controller, which is a programmable universal temperature controller that has two outputs (so dual stage)
It can be programmed for many steps over many weeks and can even do (slow) temperature ramps (up or down)
It is actually sold as a Brew controller, but because of it is easily programmable it can be used for many purposes.
great article. But I need HELP. I bought a stc 100A. worked fine for the first week and now I can't get temps below 52 F in my keezer. Can't find any instructions, but kinda sorta followed the ones for the STC1000. Should I just buy another controller [very limited budget] or can someone tell me what I'm doing wrong. The You-Tube video involving a fish tank wasn't helpful.
thanks for your time
Very nice article. I just wanted to chime in and recommend against placing the temp probe in a jar of water in the ferm chamber. I actually initially did this for about 3-4 batches when I first began using a ferm chamber (freezer and a ranco digital controller [now an inkbird]). In concept it is a good idea to keep your ferm chamber from rapidly cycling on and off due to having the probe in the ambient air, susceptible to large temperature swings. However, the problem is that it does a very poor job tracking and combating the heat given off by fermentation. In other words, your fermentation bucket/carboy will rise 5-10 degrees above ambient as it enter peak fermentation. The heat produced thereby gradually warms the ambient air in the ferm chamber. That ambient air then very slowly warms the jar of water. When that jar of water finally warms enough to trigger your controller and start the cooling cycle, your bucket/carboy temp is already 5-10 degrees higher than you want. Then, the cooling cycle kicks on, and continues to cool until your jar hits your setpoint - but at the same time, the volume in the fermenter which is 50x the volume of the jar [and which also has the heat from fermentation] has likely not noticeably cooled. So while the jar method has the advantage over putting the probe in the ambient air, in that it provides greater buffer, since that buffer is independent of the heat source, it actually decreases the ability of the ferm chamber to counteract temperature swings in your fermentation chamber. In fact, in my opinion, a water bath or a ferm chamber set at a static temp several degrees below your desired fermenation temp would probably be better than a ferm chamber using the jar method, in that at least the former methods eliminate the temp swings/excessive heat spikes you get with the jar method. All that to say, if you don't have a thermowell, just find a way to slap your temp probe to the side of your fermenter with some sort of insulation...that way your fermentation chamber is directly controlling the temperature of the wort with little to no delta.
This is what I used for a Thermowell. http://www.homedepot.com/p/Homewerks-Worldwide-1-2-in-x-20-in-Chrome-Plated-Copper-Faucet-Supply-Line-7226-20-6-12-2/203672694
Only about $7 at Home Depot. Just pinch the one end and solder the seam. Drop through an opening in your fermenter, and drop the thermocouple from the temperature controller down the tube. Nice close fit, so there is good thermal accuracy.
Does the ceramic heat lamp produce any wavelengths that could be detrimental to the beer? A lot of reptile bulbs are designed to produce UV.
bought an inkbird itc 308------just want to turn on a fan when my garage gets above 85 degrees-
programmed it [i think] with the set temp--plugged my fan into the 'cooling' plug--
it turned on the fan when it went above 86 degrees--but when the temp dropped down to 75 the unit 'heating' light came on, and the cooling light went off [nothing plugged in to heat plug] and the fan kept working [my cooling device]-
i obviously have some other parameter set wrong--can anyone give me specific settings for all of the possible settings ?--Thanking You in advance--hh