All systems in a home (heating/air, furnace, hot water heater, piping) have to be checked periodically for performance and maintenance. If you are buying a property in Winter you can check for a few signs of the performance of the systems. Based on what you would have already seen and found out on issues 1-4, you will know if the systems of a house are having to work over-time to keep a property heated. You can also check for certain winterizing techniques to know if the owner is serious when it comes to the maintenance of the systems. Check the filters on the furnace to see if they are clean, dirty or have any signs of recently being changed. Check the water heater to see if it has a thermal blanket to assist in keeping water heated inside the tank. Look at the outside A/C units to see if they are covered to keep out the winter elements. Take a special note of the water faucets outside the property to see if they are properly insulated and covered.