Double glazing your windows is most effective at retaining heat, but if you don't want to replace your old sash windows just yet, you can save energy by stopping drafts. Seal or caulk any gaps around the frame using a sealant gun and cartridge - your local DIY or hardware store should be able to advise you on the best type for your needs. But whatever sealant you use, first ensure that all the surfaces are clean and dry and that there is no loose or flaking paint which could prevent the sealant adhering.Fit weather strips to opening windows and doors - these come in many shapes and sizes ranging from cheap and easy to fit self-adhesive foam rubber strips to more expensive but durable plastic or metal weather stripping. Prevent drafts under doors by installing an adjustable threshold or brush type strip at the bottom of the door.