All our Hydro-to-Heat-Convertor models work on the principle of natural draft.
The combustion process is a staged combustion with catalytic after burn. The staged combustion is composed of pilot air, top/down primary combustion air, pre-heated air over the window that acts as primary combustion air or secondary combustion air depending if you are at the beginning, middle or end of the burn cycle. Pre-heated secondary combustion air is introduced above the fire via the Hot-Air-Box technology.
This pre-heated secondary combustion air will burn off most of the unburned combustion gasses. Before the flue gasses hit the internal water heat exchanger they need to pass trough a catalytic combustor that will burn of the remaining of the unburned volatiles and particles at a temperature as low as 400F The firebox is fully lined with silicon carbide refractory material that has a dual function: one, maintaining a high temperature inside the firebox of around 1,500F and second, allow for a good heat transfer to the water in the water jacket by means of direct contact between the silicon carbide bricks and the steel water jacket. Silicon carbide refractory has a 12-times better thermal conductivity then regular 1st quality firebrick used in regular wood stoves.
All our models have a relative small water content of between 5 and 25 gallons. We do recommend the use a storage tank of 100 to 200 gallons to achieve optimum efficiency.