If your furnace is more than 15 years old, or if it is having frequent problems, it may be time to replace it. Some signs that your furnace may need to be replaced include:nn-Your energy bills are increasing, even though you are not using your furnace any more or less than usualnn-Your furnace is making strange noises, or is not operating as quietly as it used tonn-Your furnace is not heating your home as evenly as it used to, or is not keeping your home as warm as it used to