Most places don't need aquarium heaters during summer. If you live in Canada or Alaska you might, but it depends on how cold the house is during the warmer weather.
Even in the UK, members are having concerns about the water temperature in their tanks going over 26C. I find that funny because here in Australia that is a normal temperature in spring and the tanks hit 30C+ in summer
Then you get other places like Thailand where the water sits on 30C+ all year round.
Most tropical fishes and shrimp are fine in water with a temperature between 18-30C (64-86F).