I recently had a new furnace installed in my house in Western NY State. The furnace is an Amana AMV90704, a 96% efficiency furnace with variable speed ECM blower. My wife and I are very happy with the choice and we look forward to saving on our utility bills versus the 20 year old 80% efficiency furnace it replaced. I have a question regarding my new furnace and using it with an auto setback thermostat.
We had a couple of contractors in to look over what we had, see the furnaces that they had to offer and so on, and we heard a couple of different opinions regarding whether or not to actually use the auto setback function on the thermostat with the variable speed ECM blower condensing furnace.
One contractor told us that this furnace would use less electric/gas in the long run if we left the thermostat set at a constant temperature, so that it would run all day at, what he said would be, about 40% capacity. He suggested that it would use less fuel this way as compared with turning the heat down, say 5 degrees, overnight and while we were at work during the day, and forcing the furnace to fire at full capacity in order to heat the house back up again at the end of that cycle.
Another contractor we asked, and everything that I've found on the internet, indicated that we'd save more money by utilizing the auto setback function of the thermostat, turning the heat down 5 degrees while we're asleep, and while we are at work.
I would love to hear what you know on this topic: whether we'll pay less in utilies (gas & electric) by keeping the temperature steady, or by turning the heat down 5 degrees at night. If you are aware of any research that compares the energy use of these two scenarios, please direct me to where we could read up on the topic, particularly if the conclusion is the first option (keeping the temperature steady). If you need more specifics on the furnace that I'm referring to, please let me know, and I'll see what I can come up with.
Thanks in advance for your help. I look forward to hearing your responses.