Thank you for your explaination. Don't have to bother think about it any more.
a furance cost 5000. It should last 20 year without problem. 5000/20 = 250 year
250/12 = 21. dollar .
Most time furnace problem is caused by some water in the sensor tube. too much dust on the fan.. all easy DIY.
You should buy the plan if you can't use a srewdriver or it is over 20 years and you don't have the money to replace it. But it is waste money for most. I would replace the furnace when it is about 20 to 25 years old.