I'm not sure exactly how old my furnace is, but it's avacado green, so that tells me "made in the 70's". Remember those lovely "earth tones" of the 70's, fellow oldsters? Appliances, shag carpet, dishes ... all in "harvest gold", "avocado" or the lovely "coppertone".

So I'm sure it's 30ish years old, and still going strong. Thankfully.

My friend just got a new furnace/central air, and it was around $6000 too. Seems to be the norm.