fermentation temperature

I don't have a good way of controlling fermentation temps, normally I just stick it in the closet and crank up the a/c. I've always assumed the carboy is about 5 degrees above ambient. But on my current brew I decided to check the temp of the bowl of starsan my blow off tube goes into, which is a couple degrees below ambient. Now, I know that while fermenting, there will be a certain amount of heat generated, so as long as I take this into account, will taking the temp of the starsan be a more accurate way of monitoring the temp? There is probably a bit under 1/2 a gallon of starsan and my carboy is holding 5 gallons but I don't want to open up my carboy for a temp/gravity reading until fermentation has died down.

I think without putting that carboy or bucket in some cold water it's gonna be too hot in there regardless of having an a/c on.......I'd put it in a large cooler and tape/velcro a thermometer right above the water line.....

Measuring the side of the carboy will be more accurate than measuring a bowl of StarSan.

stick on thermometers for your carboys or buckets during fermentation. Ive noted different wort temp rise differently with different beers and or different yeasts so it's hard to really put a solid figure and say 'wort is usually so many degrees above ambient temp'.

I use a home thermal leak detector. It's not good for mashing/ boiling because it measures the surface temps off the foam and the pot, but it works well for this.

I would recommend the fermenter in the water method. You can put a frozen bottle of water in there a couple times a day to keep the temp down, I did that before I got a chest freezer and it works great and its nearly free. I ferment most beers around 61 degrees ambient/water temp and they always turn out great.