So, I am getting quotes to replace my furnace (Minnesota). First recommends the Lennox G61V; the second recommends the Brant Plu 90i. So far, so good; they are both two-stage, variable-speed blower models with comparable efficiency. Here is where I get confused.
The Lennox guy claims that a single-stage thermostat is all that is needed. The furnace automatically runs for a set time at low and then kicks up to high, and this will satisfy all needs. I am doubtful.
The Bryant guy claims his furnace has a patented control board that learns from how often the thermostat calls for heat and adjusts the low-high cycle accordingly (perhaps even eliminating the low cycle period to fire off immediately at high). He states this is better (than Lennox) and will work great with a single-stage thermostat. He practically blanches when I tell him that we set our night-time temperature to 55 with the call to come back to 68 at 6:30 a.m. (via an older setback Honeywell Chronotherm). Something like "this furnace is designed to work for keeping the temperature at a more even level (not more than, say, 5 degrees between night and day) and might not be a good choice for your setabck." (By the way, the house gently coasts down in temperature at night; I doubt that it ever reaches below 60 before the calls for morning heat are issued).
OK, so my questions are:
First -- It seems that to really get the most out of either of these furnaces, I need a two-stage thermostat. It seems that the ability to cycle low-high-low for variable times is much better than the low-high-off cycle with set time intervals. What are opinions on this? Does the Bryant smart controller subsitute for a smart (i.e., two-stage) thermostat?
Second -- How will such furnaces react to a large setback at night? I would think that the thermostat (especially a smart one) would gradually ask for heat to come back in the morning, so it shouldn't matter much. Again, what is your opinion on this? Is a large setback a problem for two-stage furnaces? If so, would a two-stage thermostat remedy the problem?
Finally -- I know someone will yell at me for this (for asking an equipment-specific question), but is the modulating Rheem furnace a notably superior performer over two-stage furnaces in these situations? Or, do the issues of control and thermostats become messy to the point of over-complexity? I have tried to get quotes from a few Rheem dealers, but they have not been so cooperative (one would not venture 20 miles across town to install; one promised to call back to schedule a consult but never did), which really turns me off.