A couple of years ago, the fiance of a good customer asked me to price installing expensive oil-filled permanent baseboard heaters throughout her condo, because she felt she was paying too much to heat with her HVAC system.
I went there, did a quick look around the unit and a better look around her attic space. Then I explained how a one-time expense to reduce heat loss would benefit her more than a new way to pay forever to replace the escaping heat.
There were loose duct connections, sloppy and missing insulation, and the furnace needed a good tune-up, as evidenced by the yellow flame. I recommended an HVAC technician, an insulation specialist, and to look into new windows.