A radiant heating system comprising a substantially hollow housing having detachable baffle plates internally positioned within the housing. The housing has an inlet and outlet for a flow of coolant to enter into and leave the housing, and a top plate sealing the upper surface of the housing has openings defined therein for insertion of heating elements to project into the housing and be in direct contact with the coolant to heat it. The inlet and the outlet are interconnected with piping to form a closed fluid flow circuit. Two or more baffle plates are used to increase turbulence of the coolant within the housing as it flows through, and temporarily keep coolant in the housing longer to heat it.