Heat produced as a by product of fermentation?

I made my first 5 gallon batch last night with my new brewer's best kit. I did everything the directions said and cooled to wort to 70 degrees, added luke warm water to the 5 gallon mark and pitched the yeast. I put it in the upstars closet and stuck my liquid crystal themometer on the side of the fermentor (plastic bucket). I went back to check the temperature a little bit later and it was at 80 degrees! I was worried and confused since my house isn't that warm, so I put my empty carboy in there too with the liquid crystal thermometer and the closet is at like 68 degrees. The airlock was bubbling away this morning after only like 8 hours in the fermentor, so i'm assuming it's fine. The temperature has dropped to the mid 70s. So is heat produced as a by product of fermentation or did I screw something up? Should I be going for 68 degrees in the fermentor or 68 degrees for the room it is in? Thanks!

Fermentation is definitely exothermic- I've heard of increases as high as 10 degrees in actively fermenting wort.

You want the wort temperature to be 65-68 degrees, regardless of room temperature, if that's the temperature you're shooting for. Higher may cause some esters (fruitiness) and/or some fusels (harsh alcohol flavors).

I like to ferment my ales at the cool side of the yeast strain's recommended temperature, so sometimes my room is at 60-62 degrees.

Heat is produced, and the more vigorous the ferment, the more heat you can get. This is why many people end up acquiring a fermentation chamber where they can control the temp. I set mine at about 66-67F for the primary ferment.

You did good, the yeast are messing with ya!

My first stout went up 8 degrees using S-04. You should shoot for 68 in the fermenter or less. Most brewers say they get about 4 degrees rise from the room temperature. Once fermentation is over or slows you'll notice it starts to normalize more with room temperature. Next time you'll want aticipate for the rise ahead of time. Some folks make swamp cooler using t-shirts and a basin of water and ice bottles if necessary to maintain a good temperature.

Looks like I'll have to put the fermentor in the basement next time. Maybe even with this one when I get home, depending on the temperature. I didn't realize the temperature would rise that much from room temperature.

I'm 2 batches in, and this has happened both times. I keep my house cold enough in the winter that I wasn't otherwise worried about fermenting at too warm a temp. Until I saw the post-pitching spike.

The first time I used a tote I already had, added water, and went the swamp cooler route. A little water and a few ice packets chilled it very quickly. A few nights later it got so cool I actually had to add warm water to keep it from getting too low and slowing/stopping activity.

The second time, with a full secondary already in the closet and the tote removed, I simply put the fermenter in the bathtub, filled the tub with cold water, and left it for a few a few hours. Once it broke 75 I put it in the closet and it's been fine (and fermenting like crazy) for three days now.

Another thing to consider is the pitching temperature. If it was 70 when you pitched (I'm not sure of your temperature when you added the yeast), and fermentation started right away, it'd never cool down to room temperature. I like to pitch my yeast at my desired fermentation temperature, maybe even a little bit cooler. So, I'd probably pitch my yeast at 62-64 degrees.

Another thing to keep in mind is air circulation. If you put the carboy in a closed closet, much of the heat generated will stay in the closet and your ferment temp will go up. Put that same carboy in an open room with good air circulation and much of the heat will be quickly disapated and the temp in the carboy won't go up very much.

The lagers I have going in the basement are holding at 50 F with an air temp of 50 F. I've just got them out in the open in trays with a couple inches of water. Water is a good heat conductor so it helps to remove heat (and stabilize temp.). No fans, no wet T-shirts. Of course these are lagers and they don't generate as much heat. If I'm doing ales in the summer and the basement is too warm, I'll add the T-shirt and a fan to give me at least 4F below air temp.

Well thanks for all the great replies. I'll check the temp when I get home and adjust accordingly. I'm not sure what the temperature was when I pitched the yeast, which was another mistake. I cooled the wort to 70 and then just added what felt like room temp water and pitched the yeast. I'll definitely make sure the wort is a little cooler before pitching the yeast. I'll probably put it in the basement too, or at the very least not in a closet. I put it in there because it is obviously dark all the time. So what are the odds that I'll have some off flavors due to the higher temperatures?