Runaway ferment

I brewed a sort of imperial oatmeal stout on tuesday pitched us-05 at about 3pm and set two carboys (I do 10 gal batches) in the chest freezer and set my ranco controller to 68. 24hrs later the temp was 66 and there was a good amount of krausen, but I was concerned that the temp would drop overnight so I put a heating pad in the freezer and hooked that up to the controller and unplugged the freezer. I checked it before bed and it was holding at 68 so I left the heat pad in there. This morning I went to the basement to check on it and it was at 74. What should I do? I'm worried that if I reign it in to 68 that I'll end up with a bunch of diacetyl, and that if I don't I'll end up with a bunch of fusels. Any suggestions?

Yup, a RIS with US05 can really take off on you. I would pull the temp back some, but not too much or you may impact the yeast and not get a full ferment. Maybe 71 or so. Now you know to get another temp controller for the future at least, one to keep the heating pad running if the temp falls on you and the other to kick the freezer on if the temp starts pushing upwards.

I pulled it down slowly to 70 and I'll leave it there. I definitely need another controller especially for the winter. Thanks for your help.