I have a mauled hand and was given a demo under floor heating tile to warm my hand on. This draws around 18W and with body warmer and jacket can raise the temperature of the 30 litre fermentor 10 degs above ambulant the amount of course dependent on jacket thickness. However the big problem is the heat given out by the fermenting process its self, this is rather unpredictable so really need some thermostatic control. I can't make up my mind a cistern thermostat will clearly fit around the fermentor with easy would need to ensure temperature can be set low enough some start as zero other don't start until 40 degs but it is the gap between on and off temperature which is missing from many adverts. Room thermostats not as easy to mount but do say how many degrees between on and off to get 0.5 degs needs to be electronic type. But no gland for cables with room thermostat so rather a Heath Robinson afar. Fish tank heaters seem little on the large size min seems to be 25W and although they say fully adjustable don't give the range so again could be too hot. So what thermostats have been used and how well have they worked?