It doesn't get below freezing in Southwest Florida very often, but if freezing temperatures are forecast it is a good idea to protect your backflow.
Should this occur, your above-ground backflow device may freeze due to the location and exposure of the device. You may experience no water (frozen) or damage to the device caused by frozen internal water that may crack or warp the brass internal parts.
Therefore, the Utilities Department recommends you winterize your backflow devices to protect them from harsh freezing winter weather. The freeze usually lasts only a few hours and then it tends to warm up. For this reason, you may only need to prevent the cold from settling on your device.
An inexpensive way to do this would be to cover the devices with burlap type material and cover with black roofing felt or material similar to that used to protect flowers and plants from frost. There are products available such as a decorative fiberglass rock that would cover the device year round and be aesthetically pleasing for your property. These are available at home improvement stores. Some people cover them with recycling bins.
The responsibility of protecting the backflow devices is that of the customer. Should you have any questions on this matter, please contact the Utilities office at (941) 240-8000.