Temperature... Try and maintain a temperature between 70 and 75 degrees for your rats' enclosure, or as close to it as you can get, for optimum health. Although rats can "survive" at lower and higher temperatures, from 60 - 90 degrees, it is not very healthy for them. If rats are too cold they can develop respiratory infections, and if rats are too hot they can develop heatstroke and die. An extremely helpful thing you can do, is put a thermometer by your rats' enclosure. By checking this thermometer, it is easier to maintain the proper temperature for your rats. (Warning! don't put the thermometer in a spot where your rats can get to it and chew on it because the mercury in it will kill them.) What You Can do if Their Environment's a Little Cold... Turn up the heat if you can. If you can't... Put your rats' enclosure in the warmest room of the house (heat rises so upper levels of the house are warmest.) Make sure that your rats have a cozy sleeping den with lots of warm bedding. Yet another critical point as to why you should always try and have at least two rats. They can share each other's body heat. You can cover your rats' cage with a towel to try and help retain heat inside of it, but know that your rats will pull in parts of the towel and chew it up. Do not cover your rats' enclosure if it is a tank. You can get a heat lamp and place it next to your rats' enclosure. You can place a heating pad under half of your rats' enclosure (only half, so that they can get away from the heat if they need to.) Keep the pad at a low setting. You can use a small space heater in the room your rats are in at a low setting. What You Can do if Their Environment's a Little Hot... Turn up the air conditioning if you can. If you can't... Put your rats' enclosure in the coolest room of the house (a basement works well.) Be sure to keep the windows of the room that your rats are in shaded. The darker the room the better! You can put a fan next to your rats' cage. (A fan will not help if they are in a tank.) You can freeze a tightly sealed plastic pop bottle full of water, or fill a tightly sealed container full of ice cubes, such as a jar, and put it into your rats' enclosure. These items will need to be switched with fresh ones as they become melted and warm, so it is good to have two on hand to switch off with each other. (Never use commercial soft ice gel packs. Rats can chew these open and the gel inside is toxic!) You can dunk your rats in cool water, or place a small two inch high pan filled with an inch of cold water into their enclosure, which they can then use as a pool. (Although they may not use this if they hate water.) What is Heatstroke? Rats can easily die from heatstroke. Temperatures over 95 degrees can be dangerous. You can feel a rat's tail to tell just how warm they are (their tails are normally cool to the touch.) Signs of heatstroke include; panting, eyes wide open, drooling, laying flattened out on their belly, and unconsciousness. If you see these signs you should immediately immerse your rat, up to their neck, in slightly cool (not cold, because it could put them into shock) water. Then offer them some cool water to drink. If this treatment doesn't help, rush them to the vet!