Depends on the shrimp you are keeping. And most importantly how warm you keep your house lol. My apartment is not that warm I wear a sweatshirt most of the time but my fan is on quite a lot to keep it at 68.
Okay. I was just wondering why anyone would pull the heaters.
I had 4 different heaters before. No matter what temperature I set them (even the lowest one) they're always warmer than without a heater.
Example: I had one in my 12g tank. It was winter and the heater (with lowest setting) able to keep my tank at 76-78 temperatures. I decided that's too warm for my shrimp so I pull the plug. After one day and night of keeping track, my tank is about 75 during warmest time of the day and 70 in the coolest night time.
So in the summer I suspect heater to be working even if you turn to the lowest setting. So to be safe it's better to unplug the heater to avoid any unnecessary heats or in case of a malfunctioning heater.