For me in my location, with only running during the day time hours, bitter cold freezes up the ice over the aerators every night. It takes a while to open a hole sometimes weeks if I don't go and drill holes over the diffuses (which I hate doing!)
This season we placed some logs floating over the diffusers. They draw the heat during the day, provide a lot of surface area and allow a hole to open quicker the next day. I will be replacing them with "man made" ABS logs this weekend. I think beavers in the north have the right idea for keeping water open
