If anyone was wondering how I keep my fermentation buckets warm and at constant-ish temperature, this is your answer. The sensor is covered with a double patch of insulation so the external temperature doesn't affect it that much, and it's the cheapest under-floor heating film from china. There's 4 sections on every bucket, so 60-ish watts. With cheap insulation that's enough to keep it at 25C easy when external temperature drops to 5