Summary: To balance heating and cooling in your home create separate heating and air conditioning zones with either furnace dampers or with separate systems.
Carl, I'm getting ready to buy a house in the next 2-3 months in Texas where it gets very hot.
Is a single story house less expensive to cool than a multi-story house?
I'm renting a 2-story home now and the second story is always hot, no matter how cold the first story is. I really have to crank the air conditioning to make the upstairs even remotely comfortable.
Am I right in thinking that a single story home would be less expensive to cool, everything else being equal?
I always suggest discussing questions like this with your local energy (electric) company. They normally have very accurate information and give good advice.
But here is what I have learned over the years, building in both the south and in the north.
The reason you have to crank the A/C is that the system in your rental house is not balanced.
To balance a Heating/AC system in a 2 story house, dampers should be installed in the air supply plenums (supply air ducts) which are controlled either manually, electronically, or by temperature.
The plenum to the 2nd floor will restrict air flow to the 2nd floor during the heating phase as less air flow is needed to heat the 2nd floor as heat rises by itself.
The plenum damper in the lower level (1st floor) will restrict air flow to the lower level during the A/C phase, forcing more air upstairs where it’s needed as cold air falls.
Dampers can also be put in the individual duct work system that runs to each room to restrict air flow in some ducts, forcing more air to flow other ducts, or you can simply adjust the individual registers in each room to restrict air or not restrict air to achieve the same result.
This is the way it was done back in the early days when central air conditioning was a relatively new luxury.
It is horribly inefficient and a pain in the neck if you had to run around closing or opening dampers by hand.
Newer well built homes with modern energy efficient heating and air conditioning systems use separate systems for different areas, called zones, to perfectly balance comfort and efficiency.
Two systems should have been installed in your rental house.
Two smaller A/C systems, one down & one up would have cost very little more to install than the one larger system that is plagued with the problems you are experiencing, and would use a hell of a lot less energy to operate.
I think you'll find that the cost savings of building a 2 story 3,000 sq. ft. home will more than offset the cost of adding a separately zoned, well insulated upstairs central cooling system, which is what any 2 story home SHOULD have, even in Northern climates.
Even a one level 3,000 sq. ft. house should have 2 separately zoned systems for heat and/or cooling. That's too large an area for one system to maintain equal comfort throughout.