Check your windows
One of the most likely culprits for energy loss are your windows and doors. Pay close attention to drafts, decay and/or peeling paint and operational functionality. Drafts and increased noise means that your windows are not insulating properly and may need to be replaced. Check for increasing hot and cold spots, and ice/frost buildup. Windows that are not insulating properly can allow moisture into the home.
This moisture begins to rot the wood and may lead to water damage. The damage at the left lead to a costly repair of this wall before window installation could proceed.
Be sure to check the caulking and weather stripping around the windows and doors. If there are spaces, fill them in with new materials so your windows and doors are well-sealed. Caulking of windows, doors, and siding will pay for itself and is one of the best ways to reduce the energy costs of heating and cooling the home.