The last week has been beautiful dry weather. The other day it was actually 90 degrees. So I have had the top down and loving it. This morning I woke up to 40 degree weather. I had a 25 mile drive to work, mostly highway speed. It was a perfect time to test the heater. Despite the top being down, the heater actually kept me pretty warm. Should work just fine this winter when its -20, but with the top up.