no two zone homes with separate systems are alike...you have to by trial and error find out what works best for you as far as comfort and operating costs...you don't mention your location...I am opposed to large setbacks for heat pump systems....generally you want to minimize the use of supplemental strip heat since it is so expensive...with that in mind, I would want outside temp sensor for each system and lock out aux heat down to a certain temperature. You don't mention the type systems you have and whether they have the preferred demand/defrost or the cheaper time/temp defrost feature.

IMO

You didn't specify your location so that makes it very hard. Heat pumps typically work the best in a climate that remains above freezing most of the time. This technology has and is improving all the time to work better under freezing conditions out doors. But with that said, it is still much better in climates that stay above freezing. (32 degrees F.)

Zoning: zoning is mostly used to control temps in areas of the structure you are using while shutting down zones you are not using / occupying. While it will offer you better control of stable temperatures throughout the structure this depends greatly on the design of the system. Most notably the duct system.

Many times when zoning is implemented the duct system is over sized which when all zones are calling reduces air velocity (throw from the vents) which in turn has a debilitating cause and effect on system capacity, especially under temperature and load extremes.

Realize any system, zone or other wise... every problem with design, capacity or otherwise will be fully recognized under load extremes.

Load extremes: the coldest day, the hottest day... a house full of people (typically under the cooling load of structure.)

These types of problems are 'WHY' design of the HVAC system is so important.

I am believer in using temperature set backs but I have natural gas as a fuel. If you do set backs with your heat pumps then you want a thermostat which will not turn on the heat strips unless the outdoor temperature is below a set point.

You should use set backs during sleeping hours and/or when the floor is not occupied. As Tigerdunes stated you will have to figure out what works well in your house.

Thanks for the info. Before I put the system in I had 4 different estimates. The first guy mentioned outside sensors for the emergency heat which I thought made sense. I mentioned it to the next companies giving me quotes and the others did not use or like them. The last guy said that you shouldn't use them because they keep the auxiliary heat from coming on during the defrost cycle. I am not sure if that is true or not.

As far as the zoning goes my previous system was undersized by all accounts and each estimate I had recognized that. The current system install included updating the duct work in certain areas.

I have trained my wife when I do set the temps back to just bump it back up 2 degrees at a time and that keeps the emergency heat from kicking on.

I don't doubt that you got multiple estimates before doing the work. Choosing the right contractor for the job is like navigating a mine field these days as most HVAC companies use 'unskilled' labor to some extent for installation of the system.

The term unskilled to you likely means no experience right off the street. To me it means 1-3 years with maybe some maintenance experience etc. in other words they know just enough to be dangerous. I know of some companies here locally that have hired 'right off the street'... heaven forbid you get one of these in your house. The skilled labor in the HVAC industry is in dire straights.

The job is not glamorous and virtually 'no child' has dreams of becoming a HVAC contractor. Throw in a financial crisis of 2008-2009 and many skilled HVAC people left the field for good.

Something tells me something is not right with your equipment, the design of your system(s). If you continue to have problems under extreme weather conditions it may be best for you to get a new set of 'professional eyes' to diagnose your system(s) during an extreme out door temperature event.

" The first guy mentioned outside sensors for the emergency heat which I thought made sense. I mentioned it to the next companies giving me quotes and the others did not use or like them. The last guy said that you shouldn't use them because they keep the auxiliary heat from coming on during the defrost cycle."

It is frustrating when homeowners make buying decisions based on bad information. What thermostat do you have? Maybe it has an option of increasing the temperature differential before the auxiliary heat to turns on.

"Something tells me something is not right with your equipment, the design of your system(s). If you continue to have problems under extreme weather conditions it may be best for you to get a new set of 'professional eyes' to diagnose your system(s) during an extreme out door temperature event."

Maybe I miss spoke somewhere but so far I am not noticing any problems with my new system. I was just asking if it is wise to keep different levels set at different temps. Mainly I thought if I have the upstairs set lower then the downstairs then more of the heat from downstairs would go up and more of the cooler air from upstairs would come down, causing the downstairs to run more. That was my mane reason for starting this topic.

Ok I guess I misunderstood what you were saying.

During heat season I would say not so much, run each level at the temperature you want. Heat will rise so if you're comfortable on the upper level with just the one system running, then no harm or foul during 'heat' season.

The reason is: Heat rises. If you run the upstairs unit you may have to set it higher to get it to turn on anyway. Obviously this depends on the load of the structure... because as you know cool air falls. So if it is really cold out, you run the upstairs unit mostly to reduce the load on the down stairs unit... cool air falls... if the upstairs unit is off there is more cold air falling on the downstairs system... which contributes to the load on the system.

I would say under most scenarios this event would happen at night... so if you're asleep it likely wouldn't become noticeable until you woke up.

During cooling season this changes... because heat continues to rise... and there are only so many clothes that you can reasonably 'take off'... and the heat load happens when you are 'typically' awake.

So under cooling season you run the down stairs unit to reduce the load on the upstairs system. I usually see a few calls every so often on this where the home owner tells me: The upstairs system just runs and runs and it doesn't get cool.

I get there to find out the down stairs system is off. Some events this can be reversed it really depends on the home not to mention the load being put on it.

IE: record heat wave and you have 20 guests come over, thinking that magic box on the side of your house is going to take everything you can give it.

Now if it's heating season and you have 20 guests come over, you may be able to shut both systems off. Yeah, you and the likes of you are little heat pumps of your own design.

"Mainly I thought if I have the upstairs set lower then the downstairs then more of the heat from downstairs would go up and more of the cooler air from upstairs would come down, causing the downstairs to run more."

Everyday during the heating season in my house the down stairs thermostat is set to 70 and the upstairs is set to 68 during the hours of 7:30am and 6:00pm. This works well for me. There are times when the oven and stove are going full blast in the kitchen and the downstairs goes to 71 degrees and the upstairs is sill at 68. Then there are sunny days where the upstairs temperature rises due to the heat gain. On those days the outside temperature may be in the 40s and the upstairs furnace never turns on during the day.

Set up your setbacks and make some observations. You may be pleasantly surprised how well it works.

The fuel cost effects of zoning and set-backs are highly dependent on the equipment and the nature of the structure. In highly -insulated, well-sealed homes heat flows from room to room much faster than through the envelope so zoning will be mostly to adjust for changing needs for the different parts of the home from hour to hour and season to season (sun load and such). In poorer structures, savings might be significant.

Set backs with variable-output heating and cooling equipment can be counterproductive. It depends on the same factors as zoning and the length of the set back. In high output mode, heating and cooling can be much less efficient so if the controls (thermostat and other controls that may be part of the boiler or furnace) can be set up to do efficient recovery (not at 100% output), you have a much better bet on making set backs work to save money. The 2 degree bumping up would drive my wife nuts. Learning thermostats with outdoor thermometers that can be programmed to reach a specified temp at a specified time have been available for a long time. They adjust according to the outdoor temp and avoid hitting expensive fuel. (If it is near design temperature, they won't even go to lower temperatures in the set-back period.) It is easy to use these if you are on a very regular schedule. If you are not, you might have to go back to the 2 degree ramp up depending on the t-stat, but there may be an accessible setting that does not use back-up heat.

My heat essentially goes off in the daytime when I am not home. If I come home early, it does not take long to warm the place up because I have, redundant heating systems. In addition to that, they are both oversized since I live in a warm climate.

The 2 degree bump doesn't bother her because it is sitting on 65, and we usually only go up to 69 or 70 so she only typically hits it twice and it's good.

The weather in Indiana varies so much from month to month it is really hard to compare one to the next. It is uncommon to go two or three months in a row with consistent temps where I could do set backs one month and not do them the next and then compare usage. And I didn't realize there were so many factors involved in whether or not it was worth it.