This electric heating belt can help to maintain minimum fermenting temperatures in cold rooms or basements. Fits 5, 6, or 7.5 gallon plastic buckets and 3, 5, and 6 gallon Better Bottles; although the Brew Belt will also fit 3, 5, 6 and 6.5 gallon glass carboys, the manufacturer does not recommend using it with glass fermenters. Recommended use is for up to 8 days of primary fermentation.