The original contractor told me he was supposed to red tag it and turn off the gas. I told him not to do it since it was in the Twenties here yesterday. He took a Poloroid picture of the furnace and turned off the Emergency Switch on the wall. He told me he was doing that and it was up to me what I wanted to do. I did see the hole in the exchanger, it was large enough to slide a penny or nickel through it sideways and was at the far end of the enclosure.
After having it inspected today by the gas people and being told even more emphatically not to use it I turned it off and signed a contract with the people who quoted me the Lennox furnace. I live in SE VA and our winters are generally mild and not as long as the North. Considering I don't plan on living here much longer the extra price of the 90% efficiency furnace wasn't worth it to me. Besides I assume the outside unit will be ready for a replacemnet soon also. Two summers ago I had to take the fan apart and drip some oil down the shaft to make it stop squeeling. So far it has been working fine but you never know.