I have a set-up
where I can monitor the fermentation temp inside the fermenter using a bimetal thermometer that i calibrate right before I set it.
Most of the time femrentation temps run ~4F (give or take a degree or two) warmer than ambient temps. But everyonce in a while it goes nuts. That's why i watch it closely for the first 24 hours and adjust the ambient temp accordingly. I did an English IPA last Feb. I wanted it to ferment on the upper edge on the yeasts (wlp005) temp range to get good attenuation (005 is highly flocculant). I pitched at 68 that night and in the morning it was 78F in the fermenter! It ended up like a belgian IPA. Lots of esters, phenolics, and even some fusel alcohols. It was vile. it was some crazy s^$*t.
When it is a few degrees higher it is easy to bring the temp down. When it is 10F higher....It's like trying to move my fat ass when I'm drunk.