As of March 2015, Rinnai's direct-vent wall furnaces offer annual fuel utilization efficiency ratings ranging from 80.6 to 83 percent, which meets the minimal criteria for furnace efficiency. The company's condensing boilers have AFUE ratings of 95.5 and 95.6 percent, placing them in the high-efficiency category.
While Rinnai's wall furnaces are only slightly above minimum efficiency standards, they are still far more efficient than older models. In addition, their in-wall design and direct venting comes at the cost of efficiency. Furnaces are inherently less efficient than boilers, and smaller units typically aren't as efficient as larger ones. While this relatively low efficiency makes them more expensive to run, their low cost and easy installation make them viable options for some homeowners.