You do need a heat exchanger if you have an open flame waste oil burner. A heat exchanger is a device used to exchange heat from 1 source to another. An open flame waste oil burner emits large amount of heat from its open flame, by burning used oils like vegetable oils, hydraulic oil, brake fluids and motor oil. In order to make use of this heat, a heat exchanger should be connected to the burner. The heat sent to the heat exchanger is transmitted to water, and the heat of water is used to heat buildings in winter. This method of heating is very cost-efficient compared to using other fuels.