The Forge is insulated to keep the water cold during summer. During a cold winter, the insulation will offer protection against frost, but not against deep, bone-chilling cold. Eventually, Mother Nature will freeze the water inside your Forge.
That's not a problem in the unfiltered models, because the Forge is built to handle the expansion of water as it freezes into ice. However, a filtered Forge must be protected from freezing. The filter, the pump, and the connections we use in the filtration equipment will crack open when winter turns the water inside them into ice.
Our customers in northern and mountain climates keep their Forges inside during the winter.