I am an operations director for a church. Our church building was built in 1986 and expanded in 1995. Originally there were small a/c units for the building, but after the expansion two 30 ton split gas furnace units were installed in 1991. My question is they are on 24/7, they are trane units, had no real problems, have regular maintenance. Our PNA states their useful life is 15-20 years. Our finance council is concerned that they may go before that time and has asked us to get bids. Can anyone tell me the useful life of these units, as this would be a huge expense for our parishioners is not necessary. Because of the age, I've been told we cannot change to programmable thermostats this was the opinion of the vendors.