I have a Heil furnance that has sticker on it with the date of 1983. For about a month I noticed it wasn't heating as good as it had in the past. Once in a while outside my home I could smell that sulfur smell. I finally called the gas company and they came out and checked the smell. It was coming from the venting from my furnance. It is a 90% high efficiency furnace. The gas guy said I needed to have the unit cleaned out. He said I could do it myself so I did. Before I cleaned out the heat exchanger I noticed that when the burners were lit, they were rolling back to the front of the unit and looked like it was fighting for air. I had a repair guy come out and take a look at it and he said that I had a cracked heat exchanger. I am moving out of this home in month and selling it to another friend of mine. I don't want to have to spend a bunch on a new furnace but I don't want to leave him high and dry. I basically want to get it fixed as cheap as possible but yet have it be done right. I am pretty handy and fix a lot of stuff. I was wondering if it is possible to just replace the heat exchanger and what that cost would be or if it is just better to replace the furnance. I don't really want to spend the money on a new furnace when I am moving out in a month. Any advice would be helpful. Thanks.