PURPOSE: To facilitate a preparation of heating operation and reduce a cost by a method wherein a coal heating unit and a petroleum stove are combined with each other to make a hot water circulation system.

CONSTITUTION: A coal heating unit 2 and a petroleum stove 8 are combined to make a hot water circulation system. A discharging lid (cylinder) 3 is used for an additional room heating and a radiator 14 is applied in a range from a small-sized heater for an automobile to a large-size floor installation type in compliance with its use and from 6-hours for a bath to 12 and 24 hours (household and agriculture) in a wide range of applicable scope. In place of petroleum stove, other burners are used. Liquefied petroleum equipment and gas equipment may also be used together. If the discharging lid is removed, it can be used as a briquette heating unit. Briquette is fed into a briquette container, ignited and then put into a coal heating unit. In order to make hot water, the petroleum stove is ignited and if the water is reached to a desired temperature, the briquette is used for keeping the temperature.