Temperature buffer of water bath

I was wonder if anyone can help me out with a couple question regarding water baths

How much does a water bath buffer the temperature of the actual fermentation. Say if you have a water bath at a constant 64 deg and your vessel (probably a plastic carboy) is at high krausen, how much would it moderate the potential 6-10 deg rise of a large beer. Would circulating the water help stabilize the temp even more?

How accurate are aquarium heaters at maintain temps. I live in the upper peninsula of michigan so my basement even in summer is pretty stable in the mid to low 60s but the whole house gets pretty cold in the winter the idea of adjusting the temp via water bath sounds like a good option especial to keep styles such a Belgians on the table.

Any advice or insight is greatly appreciated


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Circulating won't change much, water is a very good conductor for fermentation speed. If you wanted to chill it below ambient, pumping water down a baffle (like old baudaler (sp?) chillers) would cool it off. Open water will be 1-4 degrees below ambient, due to evaporation (based on humidity), and will even out peaks quite a bit. I noticed 12 hr lag with about equal mass of water, smoothing out hot days and cool nights, and peak fermentation. Even more water will really smooth it out.
Most aquarium heaters won't go low enough, but many are re-calibrateable. So I mis-calibrated mine, to make it run cool. That worked for me in an unheated garage (but on the west coast). Very stable temps, with all the water mass. However, expect bugs to grow in the nice warm water. Bleach or something required, and spigots would be a bad idea.
I might look at an electric heating pad ($13 on amazon), and one of the cheap chinese PIDs, and a thermowell, instead. No organism growth issues. Won't cool things off at all, however. Great in the winter, however.

I was a little concerned about the sterility issue with the water bath, but I figure a closed system like a carboy with an airlock/blowoff and maybe adding a low concentration of bleach to the water I should be able to minimize the unwelcome guests swimming around. Is it pretty big issue in your experience?

The man reason I was thinking of going the water route was the temp stability over time. Where I live the temp is pretty dynamic even day to day and I feel it might be a good/economical choice. Are the heating pads like a fermwrap or a little more generic.

That is a good point about the aquarium heater temp range I really like the recal idea just to bump the rang down a little bit


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When I did not add bleach, it got slimy over time. So make sure it is a closed system, and consider bleach or periodic draining.

Water really does help temp stability, particular with heating spikes. The more water the more stable, but then you need to consider either very large/strong heaters, or use a cooler for insulation.

As for heating pad, I use a sunbeam heating pad like you would use for your back or something. Has three power levels, and is cheap. Then I use a controller on that. Works great in winter, but not in summer.

Awesome thanks for the advice appreciate it a lot


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I've taking a temp reading of actively fermenting wort in my water bath and it was within a degree of the water bath temp. I have a large tote (big enough to fit two carboys. And use a lot of water, filled maybe a third to a half up the carboy.

My aquarium heater was too hot on the low setting, so i used a timer to turn it on and off which took some dialing in.

Now i use an stc to turn it on and off.


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Sorry what's an stc is that similar to a pid controller. Did you dial your timer in so it slowly(I imagine fairly slowly with that amount of water) cools down slightly below your desired temp and then the heater bumps it back slightly above



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simnick said:

Circulating won't change much . . .

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mclaughlindw4 said:

I've taking a temp reading of actively fermenting wort in my water bath and it was within a degree of the water bath temp.

Click to expand...

I've done tests with a thermowell in the wort and also found only a one degree difference during the most active fermentation. I'll add that circulating the water in the bath makes a difference. There will be stratification without it. This is also proven by the thermowell, but all you have to do is put a thermometer next to the carboy and then at the edge of the bath and you'll see a difference. Also, glass works better than plastic at keeping the temperature of the bath and wort constant.

Man I'm pretty sold on the water bath idea it seems like a semi cheap and effective way to regulate my fermentation temps. the ease to change the water temp and it's awesome ability to exchange heat with the fermenter sounds like what I'm looking for.


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I have tried taking temps all around my water bath. I have not noticed much of a difference. I do not use a pump, and I use a pretty big tote. I checked this a bunch at first and to me it appeared to be a none issue.

Yes, for the timer i would start with say... Two hours off, 1/2 on, would leave it overnight, the next day check and adjust to three hours off, 1/2 on. Etc etc until i found where I wanted it. A bit of a pain but it worked.

Its the STC-1000. Honestly, i think I had tighter control with the timer. The STC will swing several degrees in either direction. Perhaps there are some adjustments I can make to minimize this (it's fairly new to me)

Of course for me this time if year it 's frozen bottles instead of heater.

If you don't have a timer no sense in buying one since the STC-1000 is around the same price. As long as you are able to wire it all up on your own.
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I might add about the stratification. I use a very short kitchen thermometer. So perhaps there is stratification further down in the water that i did not detect since all my reads were surface of water.

I'll have to check this again with my stc probe.


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Water is a really great transfer medium. If we all had jacketed conicals, it would be so easy!

Odd that some are saying their aquarium heater doesn't get low enough. This is the one I bought and it has no problem maintaining 65F (reading the amazon page, that's the minimum).

If you use an aquarium heater, you have to have motion in the water. I use my stir plate taped to the side. Works great. Without it, the heater only heats the water around the heater and then it shuts off, so you need to move the water away from the heater.

I have also tested the wort vs the water bath temp and they are always close, so I just monitor the water bath temp now.

I do put a few drops of bleach in the water. I usually keep the beer in the water bath for 10-14 days and it's necessary.

It doesn't look pretty, but once you get it dialed in, it's cheap and effective.

I'm just not buying the whole motion thing. I can take the temp of the water directly over the heater and yhe temp clear on the other side and they are within a degree or two. I can't think of any possible reason why this would be different for different people. I'm going off of memory here, i won 't be using that setup til next winter. I know I checked that a bunch though specifically because of what people are saying here.

Maybe I'd get more precise control with motion? I could try that out. I def don't have hot and cold spots though.


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I would think for winter use, a heating pad and a sleeping bag would be more than enough to maintain accurate temperatures. I use a heating pad, but I have a highly insulated box the fermenter sit inside of.

mclaughlindw4 said:

I'm just not buying the whole motion thing. I can take the temp of the water directly over the heater and yhe temp clear on the other side and they are within a degree or two. I can't think of any possible reason why this would be different for different people. I'm going off of memory here, i won 't be using that setup til next winter. I know I checked that a bunch though specifically because of what people are saying here.

Maybe I'd get more precise control with motion? I could try that out. I def don't have hot and cold spots though.


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What type of heater are you using?

For heating alone is the built in thermostatic control decent aquarium heater good enough to regulate the temp. The main reason for this project is to stop the temperature variation of my house and to be able to slowly cheap up the temps of certain strains(mostly Belgian) to get the desired eater and phenol profiles


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Most of the year my basements ambient temp is pretty ideal for clean American/British ales and if the water bath itself will moderate the temp at high krausen then that's half my goal accomplished


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sksquibbs said:

For heating alone is the built in thermostatic control decent aquarium heater good enough to regulate the temp. The main reason for this project is to stop the temperature variation of my house and to be able to slowly cheap up the temps of certain strains(mostly Belgian) to get the desired eater and phenol profiles


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Click to expand...

I rarely use my aquarium heater nowadays (make few Belgians or high temperature fermenting beers), but it did work fine whenever I wanted to use it. It's a small 15W heater that I got cheap. The key is having plenty of water, so that the temperature is equalized throughout.

For variations in temperature in the summer, a water bath makes it easy to maintain a steady temperature, even though it's in the 40s at night and 80 during the day (like today!).

Awesome I work one last night shift tonight so I think I have a little project for tomorrow. Thanks everyone for the awesome info. I have a 2L starter of wyeast 3711 buzzing away right now so maybe these next few weeks I'll see I I can play around with a heater and hit the temps I want. I figure that strain is a pretty good one to dial it in on since it's pretty forgiving


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Haha very true Yooper you know where I'm coming from. Add an old house with poor insulation and a furnace that looks like an SiFi writers impression of a robot octopus and keeping a happy environment for yeast(and other occupants) can be tricky


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sksquibbs said:

For heating alone is the built in thermostatic control decent aquarium heater good enough to regulate the temp. The main reason for this project is to stop the temperature variation of my house and to be able to slowly cheap up the temps of certain strains(mostly Belgian) to get the desired eater and phenol profiles


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Click to expand...

sksquibbs said:

Most of the year my basements ambient temp is pretty ideal for clean American/British ales and if the water bath itself will moderate the temp at high krausen then that's half my goal accomplished


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Click to expand...

Yes, it works great for stabilizing the temperatures.

mtnagel said:

What type of heater are you using?

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I have a 200W aquarium heater.


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