There are a great many websites on the net that simply tell you have to accept this because temperature swings in a home a normal. Hot air rises and therefore to get the downstairs comfortable the upstairs must be uncomfortably hot and to get the upstairs comfortable the downstairs must be uncomfortably cold.
Sure hot air rises and cold air sinks and there will be a temperature difference between the upstairs and downstairs. That temperature difference should not be more than 3 degrees for a system that is installed correctly to address this problem. My house isn’t and I have vaulted ceilings upstairs and downstairs with a single manually zoned system.
You must have oversized ducting and access to that ducting for the least investment possible. You can do it with enclosed ducting, but it cost more and is more difficult to install. The ducting must be oversized because in the winter time you want more air than necessary to heat the downstairs (the heat is going to rise) and in the summer you want more air than necessary to cool the upstairs (the cool air is going to sink). If the ducting is not oversized then you cannot manipulate the air as easily and as cheaply.
These dampeners can be manual or electric. They can be zoned by manually moving the dampeners twice each, once before the heating seasons and once before the cool season, or automatic through the use of a zoning system and multiple thermostats. I have manual in my home although the auto zone systems we install for our clients are dearly loved and trouble free.
In the winter you want most of the air returning to the furnace from the lowest portion of the home to get rid of that cold zone at the floor level and in the summer you want the majority of the air returning to the furnace from the highest portion or the home to help create convection currents and eliminate hot spots upstairs. These should be auto zones and wired directly into the thermostatic controls. You do not need a separate zone board or any elaborate circuitry for this. Each of these returns should be set to close to about only 25% of their opening while the other zone is 100% opening.
Sounds expensive doesn’t it? While the initial investment in a natural gas furnace with variable speed technology is more, the daily operational costs of this type of furnace greatly reduce its cost. It is cheaper to operate in heating mode, circulating mode and air conditioning mode. The circulating mode is what makes it the perfect furnace for 2 story homes. About 20 minutes out of every hours 24/7 the blower motor in this variable furnace will be set to come on to circulate about 500 cubic feet of air per minute. This helps to even out the temperatures between the upstairs and the downstairs in a whisper quiet mode while only costing about $5 a month operate. The multi-stage heating enables a longer heating cycling rather than the all or nothing blast from a standard furnace. This helps to gradually bring up the temperature of the home and allows the air between the upstairs and the downstairs to mingle and become closer in temperature to each other.