Low emission combustion system

A method of controlling nitrogen oxide and carbon monoxide emissions from a combustion system of a fuel-fired apparatus, the combustion system including a fuel-fired burner operative for generating a flame extending substantially axially outwardly from the burner;

• and a heat transfer tube having an inlet, an outlet, and a gas flow conduit extending therebetween, the heat transfer tube disposed opposite the burner whereby the flame extending from the burner passes into a flame inlet section of the gas flow conduit of the heat transfer tube, said method comprising:
• disposing a radiator within the inlet section of the gas flow conduit of said heat transfer tube, the radiator body having a thermal mass sufficient to reduce peak flame temperatures in the flame inlet section to less than about 2800 F.;
• and
• oxidizing carbon monoxide within the gas flow to carbon dioxide in the presence of a catalyst disposed within the gas flow conduit at a location downstream of the radiator body whereat the gas flow passing over said catalyst has a gas temperature in the range from 850 F. to 1300 F.