A gas-air mixer assembly is described that helps mix fuel and air within an HVAC system. The mixer assembly can also achieve lower pressure drops than seen in other solutions. A mixer assembly can comprise a mixer body through which air is supplied. An orifice body can extend into the stream of air within the mixer body and then point upstream. A tip of the orifice body, disposed in the airstream, can provide fuel through one or more orifices. The flow of air around the orifice body helps to cause mixing, as does an elbow bend in the mixer body, downstream of the orifice body.