Monitor room temperature
Ideal room temperature for rats sits between roughly 60-85 degrees Fahrenheit (roughly 15-24 degrees Celsius), going under/over these temperatures may cause issues, we need to step in at these times before problems arise. Rats can get sick from being too cold, and can suffer from being too warm. They can even die if temperatures reach those dangerous levels, heat waves take out small pets all the time, of course sometimes it is completely out of our hands.
The first obvious move is to turn on any central air, air conditioners, and fans in the home/room. Be sure the cage is not in the direct path of a breeze, this can make rats sick easily. If we are left without cooling systems or AC in our homes, in especially humid months, we may need to find ways to ensure our rats and other pets stay safe and cool. Below are methods you can use to keep your rats cool during those hot months.
Pea Diving
Pea diving is an enrichment activity in which we toss frozen peas (and other veggies like carrots or corn) into room temp (or a bit cooler!) water. They will fish for them, and cool off munching on a frozen snack dunking into some water. This can be done in a slanted bath tub, a paint tray, casserole dish or extra large dog bowl, though it’s best starting shallow and working up to deep water gradually.
Cold snacks
Cold snacks like fruits, veggies, and frozen treats can help them cool down when it's hot! Aside from pea diving, freezing fruits or yogurt is really fun for them to eat. I often use an ice cube tray, fill with yogurt, and top off with a couple berries in each one, essentially frozen yogurt drops. You can even make popsicles at home with those molds, or use pet (make sure ingredients are rat safe) marketed popsicles!
Coco Fibre dig box
A dig box of damp coconut fibre/coco coir (I recommend Eco Earth by Zoomed if available) can actually help keep them cool! As soil is a poor heat conductor, this is an awesome and very enriching way to cool down your rats!
If you don’t have a bio-active set up, you can accomplish this through a dig box. You can even ‘plant’ herbs (Cilantro, fennel, thyme, parsley, basil, dandelions, wheat grass etc) and sprout various seeds for them to forage and munch on (pictured).
Plate/tile/water bottle method
Placing a plate, ceramic tile, or even water bottle in the freezer and then putting it inside or on top of the cage can cool them down a lot. Since cool air falls, placing them on top of the cage will cool down their cage. Having them inside the cage provides them with a cool place to lay should they choose, but many rats can actually be afraid of them. My blind female hates cold plates, she would much rather the other options, and a plate on top of the cage.
I wouldn’t place the frozen water bottles inside the cage, those are best left on top of the cage as though to prevent them chewing it and having it leak all over their substrate and such.
Chinchilla cooling stone/Lava ledges
Chinchilla cooling stones are similar to ceramic tiles, but can be purchased at pet stores. Lava ledges can attach and hang to the sides of the cage, providing jumping opportunities as well as a cool spot to perch.
Cool Hides
It is important they have areas in which to escape the natural light entering the room, especially on those very hot days. Hides such as strung up rodent balls (unsafe for advertised use, but safe to string up as a bed!), plastic hides, mason jars, sputniks/space pods, empty plastic baskets, and clay/terracotta pots/hides, can all assist in cooling them down.