I would probably think that you need a chiller or ac. I keep my tank in the basement with ac in the house and it only gets to 20 C or 68 F. Even with the tempature outside the the tank being so cold when the lights come on it still warms my tank from 76 degrees to 77.5. I dont know what kind of lighting you have but on really hot days you might want to leave them off if you dont get a chiller. jl aquatics has some good prices on chillers right now they are 15% off
www.jlaquatics.com/product/ch-ep003/EcoPlus+1+4+HP+Aquarium+Chiller+with+Dual+Stage+Co ntroller.html or
www.jlaquatics.com/product/ch-ep001/EcoPlus+1+10+HP+Aquarium+Chiller+with+Dual+Stage+C ontroller.html
I would personally get the 1/4 horsepower not the 1/8 because if you ever plan on upgrading the 1/8th probably wont be enough and its not that much more.