Brewing for the first time. Using a Wherry kit. Instructions give information about ideal first fermentation temperature. However, I have now transferred to barrel for second fermentation and it just says 'cool' place.

My questions are:
1. Is there an ideal temperature range for this stage?
2. Is it better to have a constant temperature?

I have these choices:
a. continue on the underfloor heating that is on 24 hrs a day and gives the brew 18 - 20 degrees C.

Or b. move to colder annexe without heating, currently 6 degrees C and will stay cool but fluctuate, depending on outside temperature.(in the recent cold patch, the radiator in there froze and had icicles hanging off it, even though it was on low heat! and now has a hole in the radiator, so is off!)

Or c. I could put it in another room where the temperature is cooler than the underfloor heating but fluctuates depending on when the heating is on, i.e. not a constant temperature.

Or d. Experts out there tell me the best options and I will see if I can recreate them!

Thanks, in anticipation of your expertise.