If you are worried about what the winter may bring for your reptiles regarding ambient temperatures, this post is for you.
Let me start by saying everyone is different when it comes to what they consider as 'acceptable ambient temperature' but I would say that it is generally practiced that around 70 Fahrenheit (20 Celsius) is the minimum that you should keep the ambient temperatures, assuming you're not brumating your reptiles. Ensure that your hot spot is what it should be and there is a clear temperature gradient throughout your reptiles' enclosures.
For more information on the various types of heating, please refer to my heating reptiles post.
During a power cut, it is very helpful to have a backup heat source. Some people have generators that they can use in case of a power cut but others do not have the privileges for a generator (I being one of them). Instead, I stock up on heat packs. These are packs that come in a variety of sizes which when opened, begin to heat up. They take a while to heat but they last some 12 hours or so. Usually, these heat packs are used when transporting reptiles. Please note, I use these as my reptiles are not huge. If you have a large reptile such as a burmese python, you will most likely need a generator if your electric cuts out for a long period of time. Alternatively, you can keep your reptiles warm for a short period of time by using your body heat. Place your reptile in a pillow case and hold them close to your body. The pillow case will allow air flow and will keep them from exploring around your room.
Remember to keep checking your animals throughout the cold snap to ensure they are eating, drinking, shedding, excreting and behaving as normal. I tend to handle my reptiles less during the winter as the ambients are not as high as what they are during the summer months.