I have a Carrier Weathermaker 8000 gas furnace and ac unit that were installed before I bought the property -- probably around 1996 or 1997 (based on the memory of the former owner). I have had very few problems with this, except the unit doesn't cool the converted-attic MBR suite at all (it heats ok, since heat rises). My HVAC guy says that a new high-efficency furnace with 2 zones and beefier ductwork to the converted attic would solve the problem. He says my furnace is nearing the end of it's lifespan anyway, but I realize he is a salesman. Is he telling me the truth?

Only a $300 rebate for residential units in 2011.

The problem with heating and cooling two floors with a single system: heat rises.

Therefore, you need less heat upstairs, but WAY more cooling. More heat downstairs, but WAY less cooling.

This can be overcome with a well engineered damper system. However, IMHO, the best way to overcome is to use two separate systems. If you have a single upstairs room, use a minisplit for heating and cooling.

Gas furnaces have been known to last 40 or even 50 years. They have also failed in the first year. Proper installation counts most, then quality equipment.

There are way too many variables to predict when a furnace will fail sight unseen. Generalizations for equipment work the same as for people. What is YOUR expected lifespan? You can take the national average. or a local average. But you need to factor in stuff like: your lifestyle, genetics, habits, etc. you get the picture.

Yes, but according to the IRS, the entire property would depreciate to nothing over 27.5 years too -- and I'm pretty sure all of my places, which are over 30 years old, are still standing. :)

- John...

Your HVAC guy is telling you important info for any of the newer equipment - it needs larger size venting and returns, this very basic concept is skipped on many replacement lo-bid jobs and the heat exchanger flexes like a jiffy-pop pan, and then someone wonders why it never saved much money over the old iron age monster anyway.

The main problem with a older gas furnace is the efficiency is very low around 60 per cent and if the heat exchanger fails there is a danger of carbon monoxide.

The question on a older furnace is getting replacement parts and a heat exchanger if the heat exchanger fails. Some furnaces can last forty years but if a furnace fails on a cold day it is very difficult to shop around for a new furnace.

My gas furnace is 57 years old and still strong.

If I'm reading your real quiestion: how can I cool the upstairs??