All year round for me , have done for the last 5-6 years.
As ive said mamy times before, i think hot is more usefull in the summer than the winter.
In winter i find glass is just dirty, in the summer you you get more fly, bee spots, spiders poo and baked on bird poo.
You can turn up the heat in the summer which means a cleaning benifit, not just nicer to have warm water in the winter