Will my home stay warm all winter is a great question!
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If you afraid to turn on your heat because it cost too much, it might not be the heater effeciency...what about your insulation, windows and doors? If your furnace is 15 yrs old and only serviced when it quits working then you might need a new one anyway. Don't put it off...just find someone who has the tools to tell you if it's worth replacing. Ask when is the break even point? You have to compare K/watt use and gas consumption over time vs BTU and EFU rating over time.
Weather you on electric, gas or another form of heat like wood or corn pellet, you have to do some regular maintenance. Don't put off calling a local hvac guy to your home. Things like partially clogged condensate lines don't show up until the furnace is under STRESS.
A thorough inspection and cleaning is good and if you have a high effeciency furnace, you might even need your hvac guy to use his combustion analyzer. See if your really getting 95% effeciency! If you bought a car that is suppose to 30mpg and you where only getting 20mpg you would want to know why?