The new Ultra 310 boiler has been added to the Ultra family, which includes five sizes of boilers. The Ultra 310 has a combustion efficiency of 93.3%, and in low temperature applications, such as radiant systems, efficiencies can reach as high as 95.6%. This model is a floor-mount installation and is only available for natural gas. With an I=B=R rating of 225 MBH, this model works with large homes, small commercial jobs and larger jobs using multiple boiler systems.