An infrared emitter at least partially defines an interior space that at least partially contains convective products of combustion. A burner provides a mixture of combustible gas and primary air to the combustion, while secondary air is also provided to the combustion. A first side of the infrared emitter is in opposing face-to-face relation with the interior space so that the first side of the infrared emitter is exposed to, and heated by, the convective products of combustion. As a result, a second side of the infrared emitter emits infrared radiation. Static gauge pressure, measured at a location that is within the interior space and adjacent to the first side of the infrared emitter, may not exceed about 0.009 inches water column while the burner is operating. Excess air present in gasses exhausted from the interior space may be less than 300% while the burner is operating.