Great idea to keep the temperature stable. I am envisioning something like a bucket lined with a blanket and with the heater inside.Hi OlegCS - Have never used a heat mat but this one seems quite powerful. What I use are aquarium heaters that I place in a basin or kettle of water into which I stand the fermenter. so the water comes up two thirds of the height of the bucket or carboy. So the heat is surrounding most of the fermenter rather than being underneath the fermenter. I then cover the whole shebang with a heavy towel to trap the heat. The heaters I use are not thermostatically variable but they heat the water to about 78 F and I tend to use them when I am using a saison yeast or when I am looking for other yeasts to produce esters and the like that they might normally produce at lower temperatures.
As a newbie I use 1 gallon jars so I do not waste large quantities of food. Even 15-20 watt heaters can provide enough power. I really like the idea to have a thermostat. This way I'll have a peace of mind that I am not going to overheat and also it should help with the consistency.I'm cheap - I tend to use what I already have and "re-purpose". I use a seed mat under1 of the primaries and I have heating pad with 3 heat settings under another. The seed mat is designed to keep seedlings at around 70F - so it has a harder time keeping 5 gal. of must warm - I use it on smaller batches. The heating pad works great on the low or med setting - keeps 3-5 gal of must between 68 and 80F. I just check the temp when I check the ph.