To provide a greenhouse farmer with a fan forced heater with the technology for developing an environment-friendly small-scale incinerator, as the greenhouse cultivation farmer needs alternative fuel for petroleum as recently the price of petroleum is escalating.

The chip of proper amount is supplied from a wood chip storage tank 1 to a combustion furnace 3 by a supply screw conveyor 2, and fired up and ignited by an ignition burner, and then the ignition burner is stopped and the chip burns by itself. Hot air of combustion temperature of 800-900C or more flows into a heat exchanger 4, and is distributed into the greenhouse to heat the greenhouse. An ejector fan is attached to a cyclone dust collector 5 to collect fly ash by cyclone by induction so that the fly ash is not scattered to the atmospheric air. The temperature of the air discharged from a chimney, is about 100C. Harmful gas and dioxine are hardly generated.