Heating DerbyYou will lose no more heat... Quality insulation is high on the list for solar thermal engineers. Fiberglass insulation is recommended for walls and this should be doubled for attics. Insulating exterior walls with polystyrene foam is a good idea that could self finance in a few years.Do not Use Cellulose Insulation.. It becomes very inflammable when dried in hot attics. You could learn this the hard way by setting fire to the cellulose, attic insulation during a bathroom plumbing...