Q: I’ve got a two story house and only one unit, The downstairs and upstairs are always quite a bit difference in temperatures, what is the best solution to this problem? How hard is it to retro fit the house with two units?
You don’t necessarily need a second system. Over the past 15 years, we have solved this issue with 1 system in a 2 story home. Currently, all of your ductwork may be on one supply plenum. Air (like water) flows down the path of least resistance. Heat also rises, which allows the upstairs to get warmer.
Our solution is to install two plenums. The first is for all of the downstairs ducts and the second is for all the upstairs ducts with a section of round duct pipe in between on the end cap. The air will flow through the main plenum into the second plenum for the upstairs ductwork, allowing additional cooling to the second floor. This will make the air as cold or colder than the first floor when pressurized assuming the duct design is correct.
For heating, the section of pipe between the two plenums has a motorized damper, which in the heating mode, closes a percentage. This prevents over heating of the 2nd floor and better heating to the first floor.