To save energy in hot water supply, drying, heating, and power generation by raising heat efficiency by rotating the heat of flame flared up in a combustion furnace with a chimney stack removed, in the furnace for several seconds and condensing it.

In terms of hydrodynamics, a phenomenon which has once occurred does not return to its original state, crystal sugar once dissolved in water does not return to its original state, and fluid, particularly, flame once flared up cannot be stopped by an entropy phenomenon. However, in a Coanda swirling air flow using a principle of a system blowing strong jetted air toward a lower part of a part deeper than a window in a special furnace having a window at an angle around 25 degrees, and generating a swirl of air displaying a cycloid arc line wave, entropy is returned to its original state by this method. Energy is saved by efficiently gathering combustion flame, particularly using wood as fuel for hot water, drying, heating, and power generation, and reducing fuel consumption to a fraction. The flame heat is returned to photothermal coulomb from potential.