Got an APA doing quite nicely in a fridge set at 66*, but the temp strip on the carboy is like 72. I understand fermenting wort will raise things a few degrees, but my question is do i keep the temp of the wort at the suggested 68* or air in the fridge at 68?
When I talk about fermentation temp I am referring to the temp of the beer itself. Ambient air varies too much to be a reliable measure of the temp.
Yup, I leave me controller set to ~ 60 for the first several days if I want a ferment to run at 64-66
I tape my probe to the side of the vessel and insulate it from ambient in my freezer so the controller kicks things on or off depending on the temp of the probe. This allows me to keep the beer +/- 1oF from my set point.
+1. Me too. I tape the probe to the fermenter and then tape bubble wrap over the probe.
Now is a good time to insert the most accurate thermometer you have in the center of your beer.
For a long time I thought controlling ambient was good enough. It depends on what good enough means to you. I now attach under insulating foam and measure/control true temp. It has become my NEW good enough.
What +/- range do you use on your controller(assuming you can adjust)? I have a range of 7° Right now. When you put foam insulation over the probe does that change the variation of when the controller kicks on or off?
1°, but I measure the beer using a thermowell. When measuring from the side I do around 2°
i set my +/- to 1oF and with the insulation over the probe that’s where it stays.
My freezer is in a pretty cool room with a 68oF ambient so the unit really doesn’t run frequently unless I’m cold crashing a beer
+1
I run mine with +/- 1 but set the ASD to 6-8 minutes depending on how cold the fermentation is (shorter time for cooler fermentation). It’s rare I get more than a couple degrees away from the desired temperature without constantly turning the compressor on and off.
+2. I have a glycol bottle temp probe that I tape to the fermenter and then tape a hand towel over that. I keep the ambient temps at around 5 degrees lower than my fermentation target. Have had good luck with this. 
Hmmm, 5 degrees? In my case, I use an insulated cooler filled with ice/water with my glass carboy. I assume w glass, the temps are much closer inside compared to the surrounding water.
I would think that if your basically using an insulated swamp cooler set up and do a good job maintaining the water temp the actually fermentation temp is staying pretty true. I know that when I used a swamp cooler and rotated ice bottles I was able to keep things within a couple degrees.
To add to what has already been stated: +95% of the time when recipes refer to recommended fermentation temp, it refers to beer temp, so adjust ambient lower accordingly. In my experience, most standard beers up to about 1.070 will create maximum exothermic temperature above ambient temperature of about 4 - 6 degrees fahrenheit, as others have stated. How high depends in part especially on your pitching and ferment temps and the specific yeast. Of course the height of the temp swing is at the peak of fermentation. Bigger beers, especially with some Belgian yeasts the temp swing is normally 6 - 8 degrees fahrenheit.