My soon to be converted poolhouse turned garage is presently heated by an older Lennox heating/cooling unit, it presently works very well but am trying to guage how inneffecient it may be. Trying to justify tearing it out now and installing a hanging forced air or tube type overhead radiant heat vs. just running whats there until a major breakdown occurs. Near as I can tell by the serial number/model number it is a 1978, 2.5ton A/C unit (240v) and 90,000BTU gas heating unit. Model # is GCS4-311-90a-4p. The building is 36x48 with a 15' vaulted ceiling, 1 wall is R20 with triple pane sealed windows, roof is r20 , and 3 walls are cinderblock filled with vermiculite (non asbestos). Anyone have any experience with these? I am planning on using mostly for heat with little to no A/C use.