I can commet on firsthand experience. My single story had a 12 seer heat pump the first 2 years I owned it. During the third year,I built an addition and added a secound 12 seer heat pump. The origional unit now serves the bedrooms,hall,hall bath and master bath. New unit serves kitchen,breakfast,dinning,laundry,office and living area. Both have resistance back-up and are on setback t-stats. KWH electric consumption has been less with 2 units. My electric coop did an analisis based on tempature and confirmed I am heating and cooling more space on less energy. I don't reccomend a zoned single unit because few installers and service companies understand adjustments plus if a unit fails you still have part of the home comfortable.

I have a two story house with a furnace, AC condenser, and thermostats for each floor. These were installed when the house was built 30 years ago as upgrade option by the original owner.

Having a system for each floor will cost less to operate than having a single system for the entire house. First you can set back each floor as needed during the day and night. Plus each floor benefits from heating and cooling from the other floor. For example in the winter the warm air rises to the second floor which will satisfy the thermostat sooner. In the winter cool air from the second floor falls to the first. This satisfy the first floor thermostat sooner.

The best benefit is having consistent temperatures on the both floors. In the summer you don't have to set the thermostat to 72 degrees on the first floor in order to reach 75 degrees on the second floor. You save a lot of energy not having to do this.

mike,

" For example in the winter the warm air rises to the second floor which will satisfy the thermostat sooner. In the winter cool air from the second floor falls to the first. This satisfy the first floor thermostat sooner. "

Say what? ;-)

I tend to rush when I type, so my explanation comes out poorly. Let me try again.

On a warm sunny in the winter, the heat gain from the attic and the warm air rising from the first floor will be sensed by a second floor thermostat much more than that of the first floor. In the summer cool air falling from the second floor and a cool basement or slab will be better sensed by the first floor thermostat.

What happens is on mild days the system on one floor does a fairly good job of maintaining the temperature of the other floor. This is especially true if you set back the thermostat of one of the floors.

You have to live in a house with two systems to appreciate how well it works for both comfort and savings.

Salti, when he said "In the winter cool air from the second floor falls to the first." he meant "In the summer cool air,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,". It's only a typo dude,I know what he meant,the op knows what he meant so just go back on the porch til someone calls you.

So what is some specific guidance on how you set your upstairs and downstairs thermostats in summer and winter?

Every household calls for different specifics but the idea is.
Useing automatic setback t-stats or manualy changing tempature setting each time the upstairs or downstrairs are to be vacant more than 2 or 3 hours then reseting on return.
Example setback programing in winter:

Upstairs
M-F 5am 75f 5;30am owners rise and prepare for work
6;45am 55f and owners depart for work
10pm 75f 10;30pm owners go upstairs to shower
11pm 60f and owners go to bed
Saturday 7;30am 75f 8am owners rise,shower&go dn stair
8;30am 60f
10;30pm 75f 11pm owners shower&go to bed
11;30pm 60f
Sunday 7am 75f 7;30 owners shower&go dn stairs
8am 60f
10;30pm 75f 11pm owners shower and bed
11;30pm 60f

Downstairs
M-F 4pm 75f 4;30pm owners get home
10;30pm 55f and owners go upstairs
5am 65f
6;45am 55f owners depart for work
Saturday 8am 75f 8;30 owners come dn stairs for the day
10;30 55f and owners go upstairs
Sunday 7;30am 60f 8am owners depart for church
3pm 75f 3;30pm owners return from church and
visiting inlaws
10;30pm 55f and owners go upstairs

" just go back on the porch til someone calls you."

Classy. First personal attack here in many weeks. That said, it sometimes happens when people post at 11:37 PM. lol

This post was edited by saltidawg on Tue, Sep 24, 13 at 8:46

"So what is some specific guidance on how you set your upstairs and downstairs thermostats in summer and winter?"

Set the thermostat to where it is comfortable when you are in that area. When no one is in the affected area, set the temp all the way up in the summer and all the way down in the winter. If you are on a reasonably regular routine, the timers thermostats will work well for you. If not, you might want to get something you can adjust via the web.

Some of the setback thermostats now have a learn feature. You just set them manually up and down for the first few days and let them learn your habits. Its simpler than picking all the times and temps through a menu.

Bruce