The DV25SG is direct vent while the RH25 is natural vent. The Empire RH heaters are less efficient than the DV (direct vent) heaters, as is the case with anything natural vent (B-vent for gas systems). With direct vent systems, the combustion chamber will be sealed from the home and all combustion air will be both brought in from and exhausted to the outdoors. This is a much more efficient design when compared to natural vent systems that rely on combustion air from the home and lose most of the heat produced up the flue. Additionally, the direct vent heater can be installed on an exterior wall with the coaxial vent (pipe within a pipe) installed on the back of the heater, running straight out horizontally while the RH series B-vent heaters that rely on natural draft will have to be exhausted vertically above the roof to establish draft.
on March 11, 2016