We have a an 11 year old two story home that is about 3600 square feet and is currently heated with a Bryant Furnace and a Lennox 5-ton AC unit (we had to replace the builder installed Bryant unit a few years ago). When we built the house the builder did not feel that we needed to have a dual zoned system. We keep the house pretty cool in the summer (about 67 degrees) so the AC runs a lot. The Lennox unit works great and the house stays very comfortable both on the entry level and the upper level. We keep the fan in the "on" position rather than "auto".
We have 2 cracks in the heat exchanger so we need to replace the Bryant furnace. We are probably going with a Lennox SL280 unit with a variable speed blower. Everything sounds great about the unit but my question regarding the variable speed is whether this will cause the upper level to not stay as cool since the thermostat is on the entry level.
With our current unit blower being "on" at full speed all of the time I'm thinking that our cooling upstairs is probably more effective. I'm concerned that if the entry level reaches the set temperature and the blower motor goes to a lower speed, the upper level will not stay as cool. My guess is the new lennox will be better in every way than the existing Byrant so maybe this wont be an issue and I know that it will be a more economical unit to run, but at the end of the day if our new furnace causes our upper level to not cool off as well, maybe we should avoid a variable speed motor.
Any suggestions would be appreciated