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Keeping Fermenters Warm


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How are you keeping your fermentors warm during this cold winter? Most yeasts are effective at temps between 68° and 88° so with temperatures in the sub 20 range I am concerned about slowing down or stopping fermentation.

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I use pex heat loops and circulation pump and use the water heater to supply the heat. I have no automation, just the water heater the hot and cold line run right above the fermentation tanks. It can get very cold in my "Barn Like" building, but the yeast keeps working.

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If your tanks are jacketed pump water through them like everyone is saying, You can also consider wrapping some sort of insulation around the tanks to retain the natural heat that is created during fermentation orrrr you could try to get something like a beefy electric blanket you wrap around the outside of the tank if they are not too large. you shouldnt need to keep the room at 72, any large fermentation will produce a good amount of its own heat.

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Michaelangelo - what size are your fermenters? That will make a difference in how much heat you will need and what options are feasible. You can try using some submersible aquarium heaters. I've used them on small batches and they work pretty well. They won't be quite as precise as you might like but they will keep you within 2-3 degrees of your target. They are only going to be feasible at small scales though, unless you use a whole bunch of them.


These are good for 80 gallons each. Will work better with totes or open top. If you have a stainless single wall, something like Hedgebird suggests will probably work better.

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  • 4 weeks later...

Sort of a thermal mental exercise ....

Fermenting 1 mole of glucose produces 76kJ of heat and 2 mole of ethanol, so 117 kJ/mole of ethanol, or 650kJ / liter of AA(absolute ethanol).

For every 1%ABV produced enough heat is produced to raise the temp by about 1.55C(2.8F). (this assumes the heat capacity of water which isn't quite true).

So lets say you have a 1000l IBC tote with 1000l fermenting to 8%ABV in 72 hours.

If the start & ending temps are the same then you need to flux the [80l*650kJ/l] 13MJ through the surface in 72 hours for an average heat output of 200 watts.

Assume the tote has 6 square meters of surface area (roughly 6 sides of 1 sq.m each), so you need to average a heat loss of ~33 watts per square meter.

Now assume you want to have a start&end temp of 20C(68F) while the ambient is -3C(27F)[my average January temp]. You'd want an insulation material with a heat transfer coefficient of [33/23] 1.4 W/m^2-K. That's an R value just a little over R-4 (in US units) !!

In real life you'll lose a fair bit of heat in the CO2 blowoff, and the heat generated is proportional to the fermentation rate and quite non-linear wrt time, but the point remains that a modest amount of insulation provides a lot of temp increase. The problem is easier in large fermenters, and harder in small, and of course opposite in Summer.

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