Clayton's low NOx burners do not re-circulate flue gas and use a main air blower that is a radial type high-pressure aluminum unit. Its pre-mix chamber is a rectangular duct with a gas diffusion pipe and mixing plates. The chamber connects with the inlet volute, which directs the pre-mixed air/fuel to the burner assembly. The unit reduces NOx to less than 12 ppmv on smaller generators and less than 20 on larger generators. It will keep CO levels below 50 ppmv, according to the manufacturer.
Clayton Industries; 937-767-2156; www.claytonindustries.com