Service tech says that I have a cracked heat exchanger. He showed me with a camera something which looked like a crack in the exchanger. He didn't check the CO levels so I'm not sure what to do. Winter is approaching here in Colorado. Should I get someone else to look at the furnace?

If it will make you feel better,get someone elsebut if you saw it, it not going to go away//the money you spend on another look-see could help on the new furnace

I have to trust this technician that I was looking at a crack in the exchanger!
When he fired up the furnace it makes a noise like something expanding and when the burners shut down you hear the same noise. This guy said it was due to these cracks. Metal rubbing against metal or something like that. Wouldn't shouldn't he have checked CO levels?

He may not have had a CO meter(may not be able to afford one). Find a reputable company to check your CO levels. Also, when the thermostat calls for heat the flames will look like they are rolling when the blower kicks on and will not be a normal bluish color.