Fireplace with a water jacket Hajduk Volcano WP-18. Water input - economical and ecological heating of the whole house and preparation of hot water. For those seeking the greatest savings in the heating season, we have created water jacket cartridges that can be used in conjunction with a central heating furnace (gas, oil) using an external plate heat exchanger. In this model, as a standard, you get a cooler that prevents overheating of the coat.