The Windows
Double-glazed windows have been proved to save about 20% off your annual heating costs. Having said that, make certain your house has a good ventilation system when replacing windows. It is advisable to use double-glazed windows with real wood frames. They might be more expensive but well worth the price.
Use the candle test to find drafts in the house. Close all the windows and doors then put a candle on the ground and watch the flame. The flickering candle suggests you are