Temperature Dropping

I have to do my fermentation in my basement, which at this time of year gets no warmer than about 58 degrees. On Monday I started a new batch (my second) and by Tuesday it was bubbling away happily. The temperature of the brew, according to the stick on thermometer, was 64 degrees and it stayed there for a couple of days. I have wrapped an old sleeping bag around the fermenter. This morning (Friday) there was still some bubbling, but the temperature had dropped to 61 degrees. I have a brew belt heater that I could put on that would probably raise the temperature up to the high sixties. Should I do that or just see how it all plays out at the lower temps?

Your temp is dropping because fermentation is slowing. You are at day 5 and many ales will finish primary in that time frame. I would consider getting it into the mid to upper 60's for another week so the yeast can finish conditioning.

Are you at your FG yet?

If it were me, I would also try and get the temps up into the mid 60s. This way the yeast don't get too cold and flocculate before their job is done.

Yeast definitely do better when they are at a constant temp vs swinging fluctuation in temperature. What yeast are you using?

If you can ensure that the temp will remain constant when you put the belt on then I would go for it and let it sit in the high sixties for the next three weeks. However, to get a better beer you really want to make sure the temp is not swinging up and down (day and night) as it really puts a lot of stress on the yeast.

It is better to be one or two degrees below the yeast range throughout the entire fermentation process or one or two degrees above the range throughout the entire fermentation, than to let it swing in and out of the range.