We also keep our little dogs inside the house for most of the day when it is hot. I cannot tolerate the heat or the humidity very well myself; so when it is hot and humid in the summer, I get up much earlier and go outside to water the garden and flowers.
That is also when the dogs go outside, and since it is cooler at that tiime of the day, they can spend more time in the yard, and then be ready to come back inside before the heat of the day arrives.
During the day, I just let them out for a quick bathroom trip and then back inside.
We also bought a small "kiddie pool" and sometimes, I will take the dogs outside and put them in the pool and let them splash around in that to cool off.
Then, they will go and sit in the shade to dry off while I am out splashing around in our little Intex pool.
After that, we are both ready to go back inside the house until it cools off again in the evening.
Sometimes, I do also put ice cubes in their water bowl to keep it cooler, and I also change out the water for fresh water more often.
