You definitely need to add insulation to the ceiling, as much as possible. Attaching ductwork to the existing HVAC system is not a good idea, and it most likely would violate the building code. Some contractors won't even do it. Adding a mini-split system is a good option but, I would first try leaving the doors open to the lanai and see how comfortable it makes the lanai. If you don't have a ceiling fan in the lanai, you should install one to circulate the conditioned air. If the lanai is mostly glass, single pane was not a good idea. You may also encounter condensation on the inside of the glass in the winter. A rule of thumb is that, in a typical house, you lose about two-thirds of energy through the roof, and about one-third through the windows. If the lanai is mostly single pane glass, you are losing even more energy through the windows.
|