I'd appreciate some advice on which of the two Lennox furnaces named (G61MPV or G71MPP) might be best suited to our situation:
1400 square foot bungalow with old (35 year+) inefficient furnace; cold air return is in master bedroom and a source of noise (in effect the furnace is directly below the opening, and with the current furnace fan, makes too much noise to permit easy sleep). We have programmed the thermostat so that the furnace does not run during the night -- which means that the morning house temperature is often below the 68-degree target. The furnace runs a couple of hours in the morning, but is set back (to 61 degrees, I think) during the day, and back to 68 for evening. So during fall/winter it never really reaches 68 until early evening.
The G71MPP sounds appealing (since the claim is that it is "one of the quietest furnaces made") -- I expect that the same claim could be made of other modulating furnaces. But -- from those with experience of the G71MPP -- will it be quiet enough to leave running through the night so that the morning house temperature is closer to 68? (give the location of the cold air return)
I'm trying to get an understanding of what a modulating furnace would do in this situation (morning temp significantly below 68) relative to a two-stage furnace -- would the G71 be any more likely to reach 68 faster than our current furnace? How does a modulating furnace determine what output level to start out at? Is the starting level different depending on the difference between current temp and target? And once it reaches 68, does it tend to stay on longer (at a lower output level) than a two-stage furnace like the G61MPV?
Also: I'm starting to get the feeling that our current thermostat (a programmable Honeywell: not sure the model number) might not be suitable with either of these furnaces: will I definitely need to get a new thermostat with the G71MPP? (or the G61MPV for that matter) Or is it likely that our current one will be "just fine"?
Thanks for your advice...