Front-end loading is gaining momentum as a boiler system design strategy, as higher-efficiency condensing boilers replace older boiler technology and system control intelligence continues to improve. The idea of front-end loading is to marry condensing boilers to non-condensing boilers. This partnership makes sense because of the potential for an outdoor reset function to push the system temperatures from condensing to non-condensing during peak demand.
Typically, a condensing boiler will deliver thermal efficiencies in the high 90% range when the system return water temperatures are below 130°F (the dewpoint for natural gas boilers). When the warm, moist products of combustion fall below dewpoint, the moisture will cling to the heat transfer surfaces and release the latent heat.