I looked into the top of the unit while it was running and you really can't see down into it for all the gunk on the exchanger. You can barely see the fire down in there. It is very clogged as he said. But, I don't buy that it can't be cleaned. The unit is pretty old and may date to when the house was built (1947?), the burner unit was supposedly replaced within the last 5 - 8 years.
Anyone with some experience like to comment??? What would be a reasonable price to have it cleaned or is it something I can do? Anything down in there I could mess up? I know it will need replaced soon but didn't want to have to do it this year as we just spend a small fortune on other things for the place (it's a small farm). I do have another contractor coming out to look at it early this week, the one that put in our A/C and ductwork. Thanks for any advice!