I am an owner of a 78 bed nursing facility in Wi. I have 4 Lennox Whisper furnaces that were installed 11 years ago when the building was first built. Up until 3 years ago I had outside HVAC companies maintain the HVAC units. I am now with an outside contractor again this year. During the fall check of the 4 furnaces it was found that all 4 are extremely rusty and 2 have cracked heat exchangers and recommended shutting one off until replaced. I care for the frail elderly and this is now a critical situation because I need to replace immediately due to weather. One company recommends the Carrier 582ta110 and another recommends American Standard aud100c945k. What advise if any on either can you give me. I need to decide today by noon.