A short length (17cm approx) 50 Watt, fully submersible thermostatic ceramic heater that is inserted directly into your beer or wine to maintain the correct temperature for fermentation in the brewing bin or fermentation vessel (It will NOT fit inside a demijohn, with which a heater belt or pad should be used). The thermostat is easily adjusted and can be set to maintain any temperature in an 17º-35ºC range. To all intents and purposes, these are effectively aquarium heaters for tropical fish tanks.
Please Note: These heaters are designed for use in fish tanks, where they are usually placed alongside the internal filter/pump system. This causes the "heated water" to be fully distributed throughout the tank. In your brewing bucket, you will not generally get any circulation of the heat (unless you VERY GENTLY stir the beer once or twice a day) and MAY end up with a higher temperature around the heater and a lower than expected temperature reading from thermometers placed anywhere else in, or on, the bucket.
This short length mini-heater can be used in standard 15ltr and 25ltr fermenting bins if making small batches of beer or wine or in 10ltr buckets for maintaining the temperature durign the steeping/primary fermentation stage of country wines. If you are making a 6 bottle wine kits in a 5ltr bucket, this heater is just short enough to remain below the water level, though you will need to cut a notch in the rim of the bucket to allow you to close the lid.