I'm not sure about the fermentation kit. Ideally, it has to ferment at around 30-40 Celsius degrees. (maybe it is one of the reasons it is so efficient as a probiotic, being at its best at around body temp.)
I put it close to a radiator at a place which is always about the right temperature. Some people put it in a black box exposed to the sun, or in an over with the light on.