An apparatus (A) for testing an associated construction material sample includes a housing (20) having an internal chamber (22) divided by a wall portion (30) into first and second portions (24, 26). A support in the housing is dimensioned to mount an associated construction material sample therein. A first burner (60) communicates with first portion of the housing for supplying a flame thereto. A second burner (80) communicates with the second portion of the housing for preheating the first portion. The testing method of an associated construction material sample includes installing the sample in the housing, preheating the housing, introducing a flame toward the sample, monitoring the flame as combustion progresses longitudinally along the sample, and recording data regarding the flame progression. The method further includes weighing fuel used for combustion in order to calculate BTU input to the test chamber, may also include using a remote (98) to actuate a recording member (94) that is selectively advanced as the flame spreads, and may further include providing a continuous window along the housing through which the flame can be viewed.