Interested in how much heat a fully fermenting primary produces?

Ahoy hoy,
Being that im in Alaska, in the winter the cross I bear is keeping my primarys at about 68F or so. I control the temp very scientifically. To be precise, the colder it is, the higher I sit the carboy off the floor. Usually, at this time of year, I have the milkcrate the carboy is in sitting on top of another milk crate.
This year with the 50 belows and such, that hasnt quite given me what i wanted. I decided to take a large styrofoam container ( a large omaha steaks delivery box), put the carboy in it, fill it with water, then use a fish tank heater to help keep the temp under control. Now, heres where the accident discovers something. I sat the primary, itself at about 66F at the time, in the cooler, then i dump in 5 gallons of water that comes out the tap at the high 40s, low 50s mark. My thermometer says 51 degrees. Alright, ready to try the heater. Then it happens. Yes, the wife and kid distract me, and, I end up going to bed without ever installing the heater. I get up the next day, and the water and primary are at....71.1F. Im just not buying it, so i remove 3 gallons of the outer water, put in more cold, and drop it back down to 65 or so. Within 4 hours, on a floor thats barely at 60F, the temp climbs back up to 71.1 and has stayed there since. That primary is generating enough heat, that, with the combo of the water and the thick styrofoam, its able to heat itself. And Im telling you, the thermometer laying against it on the outside on the floor, reads 58-60 depending on the time of day. Not the most scientific discovery in the world, as I know folks are aware that fementation generates heat, but, with this setup, I can hold 71 with ease. I prefer 68, but at this point, a constant steady temp is better to me then one that varies 5 times a day depending on the ambient temps outside.
Thought I would let folks know, it might come in handy for someone. If nothing else, I didnt have to use yet more electricity :rockin:
Anyways, this is a FYI for everyone.
I bid you all a great day!

 

140 kcal/kg of extract.
Handbook of Brewing - Google Book Search

So take 10L (2.6 gal) of a 13ºP (1.053) wort, ferment it to a 3ºP (1.012) beer, you have 140 kcal heat produced. In a closed system, that would heat the beer by 14ºC (25ºF) by my cocktail napkin.

 

well, my fermometer on my big brew fermenting right now says 72, or 73 (hard to tell!) and the ambient is 62* right next to it!

my blowoff keeps clogging, and i have had to clean and reinstall every hour or so, luckily i am home today, or there would have been a ceiling mess!

cannot imagine if i was using an airlock

 

Thanks for sharing the fishtank heater idea! I had not thought of that.
I would guess that the amount of heat given off varies with the rate of fermentation so for the few days when it is going strongest it will stay warmer, but then when fermentation slows it will cool off. That's what I have observed in my primaries. The problem is that it is the opposite of what is often recommended for ales - start on the cool side and warm up a few degrees near the end to clean up any off flavors.

 

No, the AMOUNT of heat is constant. The RATE of heat generated varies with the rate of fermentation.

 

Thanks for the report on temps my friend, I always wonder just how much the temps are raised in the primary when it is really cookin, I use the ice bath method, and usually have to keep the water at about 58f for the first couple days to maintain the 65ish temps on the carboy, dont freeze my friend, cheers