This paper studies the combustion in a heat flow in wood. Samples of beech wood were placed on a VLK-500 platform weigher, so that the rate of combustion could be determined. The rate of heat flow was varied by changing the distance between two radiant panels and the samples. The volatile pyrolysis products were ignited by a separate propane-butane diffusion flame set over the center of the samples. The change in the sample surface temperature with time for different rates of heat flow from the infrared panels is shown. Results show that the rate of combustion at the moment of ignition is a maximum, which decreases as the sample burns out. With increased rate of burnout from 0.5 to 4 kg.m/sup -2/ and a resulting increase in the thickness of the carbon layer from about 1 to approximately 8mm, the critical heat flow increases from 1.2 to 12.0 kW.m/sup -2/.