Every year I try to keep from turning the furnace on until the last possible moment. The longest we have waited was the day before Thanksgiving. This year the weather won the contest because I was sick for a couple of weeks and it got cold!
Our furnace was installed in 1971 when they built the house. We have the money to replace it, and the central air, but the plumber told us to just keep using it until it stopped working.
So, how do you keep your furnace working for decades? Maintenance.
I have severe allergies and we use a permanent allergy filter. Once a month my husband takes the filter to the car wash and blasts all of the dirt and dust out of it. If you use disposable filters, put a new one in once a month.
And every year we have the plumber come in and check the furnace. We are lucky in our area because our utility company gives a rebate that covers part of the bill.