Living on a Prayer

Thus far, this has been a beautiful, fall week. The weather has been warm and (mostly) sunny, and I love spending as much time as I can outside before the temperature turns cold for good. Well, not for good, but sometimes 6 months of winter in Canada feels like it's for good.
Anyway, despite the warm weather, this time of year always leads me to think of winter... which leads me to think of my furnace.

My furnace is old. I don't mean a little old. I mean call-the-museum-and-document-its- existence-for-the-archives OLD. It's nearly 40. In dog years, that's 280. Or something like that. Regardless, the life expectancy of a furnace purchased today is only about 30 years. Figures.

So, it's usually about this time of year I start to think about getting my furnace serviced, since I never got around to it in the spring. This leads me to wonder if this will be the year it quits. I also can't help but notice how many leaflets and advertisements there are out there for new heating and air conditioning units. What's a good deal? Should I buy now, and avoid the headache of it quitting mid-February when I'm out of town and it's -32? Do I want to drop $3000 on a new furnace right now?

Inevitably, the answer to the last question is always 'no', so I've never really investigated this any further. At the lunch table at work the other day, I mentioned this and there was unanimous agreement. "Don't replace it, if it's not broke." Makes sense. Nevertheless, my 'rainy day fund' is growing, and again this winter, I won't be touching it in case this is the year I need to make the call.

Has anyone else gone through this upgrade? What did it cost? Any recommendations?