Northern Florida can get quite cold and experiences freezing temperatures every winter. Even so, 18 seems slightly extreme.
My house in Miami, which was built in the 50's, has a fireplace. There are evenings when it comes in handy. My memory is that back in the 70's, there were times every winter that saw temps in the 30's. We haven't seen that for a while, but 40's happen every winter a few nights. In any case, I keep wood handy.
A relative in the Tampa area had a space heater for those extra-cold times. Of course, cold is relative... :’)