The next thing to investigate is your windows.
Much of the heat loss in your house occurs through the windows. The number, size, and type of windows in a house is very important. Using double or triple pane glass instead of single pane can help reduce heat loss. Some new types of windows have been developed in recent years, including "low e" and "inert gas filled" windows. These new windows are more expensive than traditional windows, but can save you lots of money on heating costs.
For more information on low e windows, check out this website:
