With over 100 tanks running, I heat the fish building instead of individual tanks. I keep the temp around 79-80. During summer, I have to run A/C to keep the building down around 80. The building has been extensively insulated and moisture-proofed. All windows were replaced with double-insulated vinyl windows. Heating the building has advantages like the filtration/plumbing is heated, I don't have over 100 heaters plugged in. Natural gas heating runs my total utility bill for the building at around $125/month (gas and electric). The bill runs a little higher during peak hot and cold months. I have about 15 ceiling fans throughout the building to keep air moving to prevent stagnating moist spots. Heating the building also allows me to keep stored water (1000gal, 500gal, and 400gal tanks) at aquarium temperature for water changes. A single blower runs all the air injectors, sponge filters, skimmers, and air stones. There are also aerating bars in the storage tanks.
Downside is I can't keep cool-water species in the building.
I also keep steel or titanium large heaters (500w-1000w) on hand in case I need to treat a tank and boost the temp during treatment.