I live in West Wales at 1200ft. Humidity is always high and we have long periods of temperatures below 0'c during winter. For several years after moving here I experienced heavy losses every winter - lovely healthy colonies in Autumn all dead first inspection in Spring; soul destroying. It came to the point 'do something about it or give up bee keeping'. I decided to heat my hives in Winter. What I did was place a 12w vivarium heater in the void, under the grid of the OMF. This has worked well for me as I have had few Winter losses since adopting this practice. I do appreciate it isn't practicable for out apiarys where electricity is not available.