Alde heater not giving enough heat

      On my 2015 t@b I was getting some heat but not enough to warm up cabin to be comfortable.     Located under back self behind head board is a container to fill with a product called glycol.   self removed by taken out two screws.   Mine was filled at minimum level.   after topping off, cabin became very warm.    Product purchased at RV store and its an antifreeze that's light yellow called glycol ?     Hope this helps someone.   Factory must have under filled it.