Hello: I am looking for some education here. I have a rental property with an old oil fired hot air furnace that has been giving me trouble for the last few years. It finally gave out last week, so I had to replace it. There was gas at the property, so I decided to change over to a gas fired hot air heater, rather than an oil fired furnace. I spoke with two HVAC guys in getting prices. One told me that a "normal" efficiency heater would vent into the existing chimney, but, since I was changing from oil to gas, I would need to line the chimney. His recommendation was to go with a 92% efficiency furnace (Goodman 72,000 BTU Upflow) and vent out the back wall rather than using a cheaper 80% furnace and lining the chimney. The second one told me that, since my chimney was already lined with terra-cotta, the liner was unnecessary. He explained that the liner would only be needed on a brick and mortar chimney (that does not have a terra cotta flue). It should also be noted that the chimney is located on the rear exterior wall of the home, and that the water heater is and always has been gas fired, and vents to the same chimney. Because the difference in price was not that great, after considering that the Utility company would give me a $300 rebate, I decided to go with the 92% furnace. However, I have a couple of questions: 1 - Who was correct? 2- Why would the chimney need to be lined simply because I am switching fuel supply? If there were leaks in the joints that could allow Carbon Monoxide into the home, the change in fuel should not change that fact. In other words, had I stayed with oil by buying a new oil fired furnace rather than a gas furnace, it is my understanding that the chimney would NOT have to be relined. That doesn't make any sense to me. 3- If the chimney did need to be re-lined, could I run an aluminum liner, or would I be forced to use stainless steel? Thanks in advance!

I need to replace my propane furnace. Should I consider a heat pump with propane backup or stay with a straight furnace? Which is cheaper to operate? I know some of this will depend on the cost of propane and electric, but are there any rough guidelines? TIA